This article is mainly going to focus on the UK, so apologies to those of you who don't deal with UK telephone numbers on the sites you maintain. The US is, however, used for comparison.

In the previous article I mentioned making sure all the numbers published online for your business are correct, i.e. the listed numbers are connected, working, and answered by whoever you expect to be on the end of the line. The article contained a table showing the types and amounts of various errors found on several randomly selected websites, but didn't discuss the figures presented in the very last column of the table, the "numbers incorrectly formatted" column. This article will address that particular problem.

Note: in examples, 'x' simply represents 'any digit'. In some cases that might be a slight over-simplification because sometimes there might be a restriction of 'only 2 to 8' or 'not zero' and so on. If you need that extra detail, please refer to the respective official telecoms and regulatory websites.

US and Canada, and a bit of history

In the US and Canada, most telephone numbers are written in a very small number of formats like:

In national notation (those without the + symbol), if the area code can be optional for local callers, then ITU-T recommendation E.123 says that you can show that area code inside parentheses.

In all formats commonly in use in the US and Canada, the hyphens and periods are optional and official recommendations are to use just spaces and optional parentheses, but the grouped 'three - three - four' format is common to all of them.

In the International Format, the '+' indicates the need to dial an International Access Code before the Country Code. In order to call to somewhere else from another country, in place of the '+' the caller would dial 00 from most of Europe, perhaps 0011 from Australia, 010 from Japan, 99 or 00 from Finland, etc. The usage of the + sign is an internationally agreed notation. Technically, there should be no other punctuation within the international format, but it is still fairly common to see parentheses around the area code, and hyphens as separators. Avoid this if you can.

For a US or Canadian national number like (303) 456 7890, the first group of three digits is the area code, typically covering a large part of one state; and in some cases a whole state. The area code first digit cannot be a 0 or 1. Prior to 1995, the middle digit of the area code was always a 0 or 1. This was how the system identified that what you had just dialled was an area code, and the middle digit zero was mostly used when the area code covered a whole state.

Having run out of capacity, and needing new area codes, the system was changed so that other digits, except 9, could now be used for the middle digit of the area code. At the same time, customers were forced to dial all ten digits, instead of just the final seven, for calls within their own area, as now it wasn't possible to tell whether the first three digits dialled were for an area code or for a local exchange code. The third digit of the area code can be anything.

Some states have multiple area codes serving the same geographical area. In this case, you simply can't dial ten digits, you have to dial an initial '1' to tell the system that an area code follows, then followed by the exchange code and the local number (a.k.a. '1 plus 10' dialling). You have to do this even if the person you are calling is in the next street.

The second group of three digits is a local exchange code, serving up to 10 000 lines. In urban locations, this can identify a relatively small geographical area. In rural areas this area may be very much larger. The first digit of the exchange code is never 0 or 1. The final four digits are the subscriber number. In many areas advertising and signs have traditionally shown only the last seven digits of local numbers. Now that many places have multiple 'overlay' area codes, this should be discouraged. Especially for anything mentioned on the web, always show the full number including the area code.

Can you tell where a number is located?

Given this simple system, Google can obviously and very easily spot a telephone number on a page, both from the format of the number and by using nearby textual clues such as a 'Tel.' or 'Fax' or 'call' prefix, or from there being an immediately prior postal address. From the given telephone number, Google can often work out the likely geographical location from both the area code and the exchange code, e.g. a number like (813) 248 xxxx is in the Tampa, Florida area, specifically in, or near, the East 7th Avenue or East 8th Avenue district. Google can try to match that location data with any other postal address information found elsewhere on the page and on other pages on the same domain. It can also determine whether that data is common to multiple pages of the site, meaning the data is probably referring to the site itself, or whether it is unique to that page (and that other pages each have different numbers listed) and therefore likely listing a set of businesses and organisations (i.e. the site is possibly a directory of some sort).

All of this information can be used to good effect in Local Search scenarios. With a fairly simple numbering system, and the small number of highly-consistent writing formats used in the US, Google hasn't got a lot of work to do to understand this information. It is possible that the number format might match with numbers in some other country, but other data on the page should clarify that the number is in the US, and of course, using the +1 prefix always clarifies this with no chance of ambiguity. The bottom line is that if you stick to the accepted formats for presenting the data, Google will understand it. Beware that numbers for VoIP lines also map to a location, but that might be more generalised to a city, county, or state, rather than to a single district.

If, however, you were to take a US telephone number like (212) 345-4567 and write it as 21234-54567 or as 21.23.45.45.67 it is highly unlikely that Google, or indeed any human, would immediately recognise it as being a US telephone number. Indeed, the former example looks like a Greek telephone number, and the latter example looks like a French telephone number. In those cases, and without other on-page clues, it is entirely possible that the web page could be mis-classified as to the geographical location of the business that it refers to.

It is also likely that some customers would not call those numbers as presented, as they might be led to believe that doing so costs a lot more than a normal call.

United Kingdom

The usage of a small range of simple numbering formats is true in the US and in most of the rest of the world - but not the UK. In the UK, there's a complication or two. The UK is divided into more than 650 areas, and numbers are not all a consistent length. Other areas are dialled using a 0 trunk code before the area code. Local numbers can be dialled either with or without the combined trunk code and area code. Area codes can have between two and five digits after the 0 trunk code, and the local number part can have between four and eight digits. Most numbers have exactly ten digits after the initial 0 trunk code, but some areas have only nine digits. Longer local numbers have shorter area codes. The 0 trunk code is omitted when dialling the UK from abroad.

The variable total number length and variable area code length confuses a lot of people. Luckily there's only a small number of valid combinations. A clear explanation can be found at Wikipedia and elsewhere. Most of the real confusion comes from the various changes that occurred in 1995, 1998, and 2000.

Wrong number!

In 1995 (PhONEday - five 011x codes), 1998 (Reading - the 0118 code), and 2000 (Big Number Change - five 02x codes), several areas of the UK gained completely new area codes and the length of the local numbers in those areas increased by one or two digits. A large number of people failed to understand these changes and have spent the next decade writing their telephone numbers in the wrong format. Obviously, if you're expecting searchengines to understand the telephone numbers quoted on your site but they are in the wrong format, this might have important SEO implications, especially for Local Search.

The major area code changes were as follows:

As you can see from the final two columns, there are at least several ways to format these numbers incorrectly. A Google search for any of those fake area codes will find tens or hundreds of thousands of sites with incorrect data:

01132 Leeds, 011 Leicester, 01189 Reading, 0207 London, 02075 London, 02476 Coventry and 0292 Cardiff

As well as lots of sites still publishing very old numbers:

01222 Cardiff, 01705 Portsmouth and 0171 London

Some of those fake formats are mind boggling. Local numbers in the UK cannot begin with a 0 or a 1. However, you can find very many examples of Southampton numbers listed like 0238 0xx xxxx or 0238 1xx xxxx and Cardiff numbers listed as 0292 0xx xxxx or 0292 1xx xxxx. Likewise, a very large number of sites list London numbers as 020xx 0xxxxx or 020xx 1xxxxx. You would have thought those basic errors would be obvious to the writer.

In Northern Ireland, all telephone numbers now fit the common (028) xxxx xxxx format, but are misquoted in a variety of ways. The code change list for N.I. is much longer than all of the above combined. The list can be included here, later, if there is sufficient demand for it. Alternatively, any detailed list (not summary, those tend to just list the Belfast changes) of the 'Big Number Change' changes will locate the information.

In the columns above, only two 'incorrect formats' per code have been shown, but in practise you are likely to come across a lot of other incorrect formats.

London

The correct format is (020) 7xxx xxxx, where 020 identifies London, and the next four digits identify the individual exchange, or provider. London also has numbers beginning 8xxx xxxx and 3xxx xxxx.

Incorrect formats regularly seen, include:

All but four of those 'mask' the real area code and all of them 'mask' the exchange code (the next four digits after the 020 area code).

Indeed, back in the early 1990s when local numbers had six digits, 0203 was the old code for Coventry (now 024, briefly 01203 from 1995 to 2000); 0207 was the old code for Consett (now 01207); and 0208 was the old code for Bodmin (now 01208).

If you ever see a site that refers to 'inner London' and 'outer London' area codes be aware that the inner/outer split came to an end in 2000 with the Big Number Change. London now has just one area code, (020), and all London local numbers have eight digits. If you see it written any other way, then it is wrong.

Coventry

The correct format is (024) 76xx xxxx, where 024 identifies Coventry, and the next four digits identify the individual exchange, or provider. Coventry also has numbers beginning 77xx xxxx.

Incorrect formats regularly seen, include:

All but three of those 'mask' the real area code and all of them mask the exchange code (the next four digits after the 024 area code).

This also applies to all Southampton (023) 80xx xxxx and 81xx xxxx numbers, all Portsmouth (023) 92xx xxxx and 93xx xxxx numbers, all Coventry (024) 77xx xxxx numbers, all Cardiff (029) 20xx xxxx and 21xx xxxx numbers, and all Northern Ireland (028) xxxx xxxx numbers.

Indeed, back at a time in the early 1990s when local numbers had six digits, 0238 was the old code for Saintfield (now 028, briefly 01238 from 1995 to 2000); 0239 was the old code for Cardigan (now 01239); 0247 was the old code for Bangor (now 028, briefly 01247 from 1995 to 2000); and 0292 was the old code for Ayr (now 01292).

Sheffield

The correct format is (0114) 2xx xxxx, where 0114 identifies Sheffield, and the next three digits identify the individual exchange, or provider. Sheffield also has numbers beginning 3xx xxxx.

Incorrect formats regularly seen, include:

All but three of those 'mask' the real area code and all of them mask the exchange code (the next three digits after the 0114 area code).

This also applies to all Leeds (0113) 2xx xxxx and 3xx xxxx and 8xx xxxx numbers, all Sheffield (0114) 3xx xxxx numbers, all Nottingham (0115) 7xx xxxx and 8xx xxxx and 9xx xxxx numbers, all Leicester (0116) 2xx xxxx and 3xx xxxx and 4xx xxxx numbers, all Bristol (0117) 2xx xxxx and 3xx xxxx and 9xx xxxx numbers, and to all Reading (0118) 3xx xxxx and 4xx xxxx and 9xx xxxx numbers.

There are no 'old' UK codes to confuse these with, but starting a number with 011 and then a space is bound to confuse US and Canadian readers as 011 is their International Access Code. They would use 011 42 to reach numbers in the Czech Republic, Slovak Republic and Liechtenstein for example.

Note too, that (011) as an area code more strongly matches places in Sri Lanka and South Africa, and that the number format (011) xxxx xxxx is an exact match used for a location in Brazil and in India. Additionally, some (011xx) area code formats match various locations in Germany and elsewhere.

Confusing signals

With incorrect formatting, could you be sending incorrect geo-location signals to Google and other search engines?

Is that restaurant in Sheffield or São Paulo?

I'll concoct an example (mainly 'cus I don't want to give a real client example), where a restaurant located in Sheffield, UK, serves south-American food, hosts their website in the US, uses a .com TLD, and the website content is in both Portuguese and English.

They just happen to print their telephone number as 011 4255 2345 (instead of the correct (0114) 255 2345 format for Sheffield). Unfortunately, their chosen format exactly matches the one used for numbers in São Paulo, Brazil.

The only other location information that Google might have to go on for classifying this site, will be the postal address for the business - but in this case perhaps the designer decided to make a fancy logo and graphic and all of the postal address information is included in that image too.

Even a beginner at SEO should be able to see that Google isn't likely to want to rank this site very highly when someone searches for 'Restaurant Sheffield'.

The only things that could save this site from oblivion are any currency clues - if the website actually contains any price information that is; and the backlink profile - being listed by multiple UK sites, or in the 'UK category' of non-UK sites.

In reality, that telephone number would likely be listed on the site using a different but still incorrect format: 01142 552345. That format matches the one used by some telephone numbers in Germany. However, in that particular case the website's "PT" content-language might be a strong clue that the location is 'not Germany' without giving any useful clues as to what the true location really is.

Why take chances with this, when getting the number format correct is very simple?

So, as well as all the hosting, domain, TLD, and the placing of text-as-text considerations, make sure you also pay attention to telephone numbers and their formatting. It is entirely possible that Google and others can normalise telephone number data before trying to classify the location, but I wouldn't want to take a chance with that.

Presently, as much as 30% of all UK telephone number data on the web is either out-dated or incorrect, or is mis-formatted. It is rare to find a website that has not made a formatting mistake, especially with the 011x and 02x area codes.

Confusing to tourists

With incorrect formatting, there are problems with local dialling in these areas. Almost everyone seems to know the simple rule 'omit the area code when in that area', and today that rule still applies in most of the world. If the area code part of a number is not clearly delineated because of incorrect spacing, then callers may omit too many, or not enough, initial digits and the call will fail. Potentially, you've just lost a customer.

Code blindness

In areas where mis-formatting has been the norm for many years, many residents will have a false idea as to what the area code really is. For those areas that now also have new number ranges coming into use, people are inserting an unwanted digit after the true area code, for numbers in the 'new' ranges listed above, and end up dialling the wrong number, e.g. for the new number (0114) 345 4567 people are mistakenly dialling 01142 345 4567 and being connected to (0114) 234 5456 instead. There are widespread reports of such mis-dialling in all of the places listed in table 2.

Additionally, not only do some people misdial new London (020) 3xxx xxxx numbers as 0207 3xxx xxxx but there are tens of thousands of these numbers misquoted in the same way on various websites. When dialled, the number will reach the wrong person as it has too many digits and the final digit is discarded.

So, not only are businesses sending confusing messages about their site to Google and other search engines, but they are also putting up barriers such that potential customers may have problems contacting them. In a recession, this cannot be a good idea!

Data Pollution

Not only are people generally becoming convinced that the incorrect area codes listed above are somehow correct, but they are also beginning to incorrectly format some area codes that have previously been without problem, or are inventing more new ways to get things wrong.

That is, someone in Manchester who is used to seeing numbers like (0161) 555 8899, will now write the Dundee number (01382) 557799 incorrectly as 0138 255 7799, as well as writing the Southampton number (023) 8044 7799 incorrectly as 0238 044 7799 (unlike most people who get it wrong by writing 02380 447799).

Someone in Preston used to seeing numbers like (01772) 445566, will write the Liverpool number (0151) 577 8899 incorrectly as 01515 778899, and the London number (020) 7755 7799 incorrectly as 02077 557799 (unlike most people who get it wrong by writing 0207 755 7799).

Someone in Cardiff used to seeing numbers like (029) 2055 7788, will write the Liverpool number (0151) 577 8899 incorrectly as 015 1577 8899, and the Northampton number (01604) 445566 incorrectly as 016 0444 5566. So far, these last two problems are very rare; but it's only a matter of time.

All these new types of error are now finding their way on to the web by the million. Some sites have built-in number formatting routines that force consistent formatting for all data. Many of these are incorrectly programmed, such that they force all data into an incorrect format.

Absurdity

If this all seems somewhat absurd to US, Canadian, and other readers, then frankly, yes it is. Perhaps 50% or more of the UK population have failed to grasp the simple numbering changes shown in the second table. A decade later, and millions of examples of incorrect usage can still be seen and are being added to on a daily basis. There are even some UGC sites that reject the correct number format of whatever you type and force incorrect formatting when the information is displayed. So, even the programmers are still getting it wrong!

When a site contains several hundred thousand telephone numbers and the majority of them are incorrectly formatted, that must surely be having a negative effect on the determination of geo-location factors for that content.

You rarely see such formatting errors for numbers in most other countries. It would be crazy for a New York telephone number to appear as 21234-52345 or as 21.23.45.23.45; but as can be seen above, many Brits format UK numbers however they like with no regard for the confusion that will cause both the human reader and the search engines.

In fact, the problem runs deeper than this. What has happened in the UK would be something like this, if applied to US numbers. Firstly, people start off by writing the New York number (212) 455 6677 in an incorrect format like (2124) 556 677. After a while, they become 'convinced' that the New York area code is (2124). When you give someone another number to call, maybe (212) 777 8899, they instead dial 2124 777889(9) where the final digit is discarded and the owner of (212) 477 7889 has to explain that the caller has dialled the wrong number. Any attempt to explain that the area code is 212, not 2124, is met with an air of incredulity by the caller.

This problem has been widespread in the UK for almost fifteen years when talking about the 011x area codes, and for almost ten years when talking about the 02x area codes. A sizeable proportion (perhaps 25% or more) of all UK telephone number data on the web is afflicted by these problems.

Google Local Search

I undertook a quick and informal survey using a number of 'local' search terms, such as 'Pub Nottingham', 'Restaurant Leicester', 'Office Furniture Leeds' and so on.

The Local Business Listings next to the map at the top of the SERPs always list numbers in the correct format - even when the entry on the underlying website does not. However, for all of the entries that did NOT have an 0845 or 0870 number, way more than three quarters of the listings, and sometimes all of the listings, in that local search box come from sites that DO list their number in the correct format on their own site or in their Business Centre listing. It seems to me that using the correct format on your site makes it easier for Google to understand it. Well, "duh", on this point I think!

There are some notable exceptions. Domino's Pizza has used incorrect formatting in all of their content for all of the (011x) and (02x) areas across their whole UK business and yet they still manage to show up in the local results one-box in almost all of the areas that they operate in. Even for those entries, it can be seen that Google uses the correct format in their local listings for those numbers. So, Google either has some ability to understand and reformat some numbers or has another datafeed with that data in, to compare and use.

I would not rely on Google getting it right for smaller businesses. If you're in London and you fail to have a single telephone number using the correct (020) xxxx xxxx or +44 20 xxxx xxxx format on your site, why would Google ever consider that it is actually based in London?

Additionally, for 02x codes, the next block of four digits immediately after the area code usually identifies the local exchange, and can home in on a very small area of a city. For 011x and 01x1 codes, the next three digits after the area code identify the local exchange. Could that help your geo-targeting efforts even more? I believe it can.

Sidenote

Most Google 'Local Search' results for the UK are listed with standard geographic numbers, but Google also shows some entries with an 084x (e.g. 0845) or 087x (e.g. 0870) non-geographic number. For the last month or more, Google seems to show less entries with non-geographic numbers, but it does depend on the type of search made. So far, I haven't seen any listed with the newer 03xx non-geographic numbers. It may also be worth noting at this point that some UK non-geographic numbers cannot be dialled from overseas. Additionally, Google used to list UK numbers in the E.123 international format, e.g. +44 116 456 5566, but recently changed to listing them in the 0116 456 5566 national format. They haven't yet added parentheses around the 01 and 02 geographic area codes; but maybe that will happen in the future?

Code does not exist

Not only is there the problem of people misquoting the current area codes listed in table 2, there is also a problem where people are quoting area codes that have never existed. During PhONEday in 1995, most UK geographic area codes were changed by adding a '1' immediately after the initial '0' trunk code of the existing area code, except for five places that gained a completely new 011x code and had an extra digit added to the local number part. Unfortunately, there are a large number of people who converted all UK numbers by adding a 1 to the existing area code, and ignored those special instructions for Leeds, Sheffield, Nottingham, Leicester and Bristol area codes. The resulting codes, codes that have never existed, are listed in the first part of table 3. There are tens of thousands of websites listing numbers supposedly using these non-existent area codes.

Likewise, for the places that now have an 02x area code the '1' was added to the old area code as a part of PhONEday in 1995, and the area code changed again in 2000. You can still find hundreds of thousands of entries online showing those old area codes. These changes occurred either ten or fifteen years ago. It is surprising that the data has not been updated or corrected during the intervening period.

Don't just take my word for it, check out these searches for some codes that have never existed:

01532 Leeds

01602 Nottingham

01272 Bristol

and others.

Ancient UK History

In the 1960s and 1970s these areas also changed to all-figure dialling and the (0x1) xxx xxxx number format, and then were changed by PhONEday in 1995 to the current number format:

(0121) xxx xxxx - Birmingham

(0131) xxx xxxx - Edinburgh

(0141) xxx xxxx - Glasgow

(0151) xxx xxxx - Liverpool

(0161) xxx xxxx - Manchester

In the 1980s, this area also changed to the (0x1) xxx xxxx number format, and to the current format in 1995 as a part of PhONEday:

(0191) xxx xxxx - Tyne and Wear/County Durham

It is a rarity to see these numbers mis-quoted in the same way that 011x codes are regularly abused, but you do occasionally see something like (01x1x) xxxxxx in print, with the first digit of the local number strangely added to the end of the area code part.

It begs the question: if most people are used to and comfortable with the (01x1) xxx xxxx format for those places, why do the vast majority of the very same people have such huge problems with the (011x) xxx xxxx format introduced in 1995 in the other cities, and in 1998 in Reading?

Indeed, between 1995 and 2000 the exact same (01x1) xxx xxxx number format was temporarily in use for London 0171 and 0181 numbers - and no-one had any problem with it back then. That format continued for a few years until the London codes were merged into the single (020) area code in the Big Number Change in 2000.

The last of these area code changes occurred in 2000, yet they still seem to be a mystery to a large proportion of the UK population.

Other UK Geographic Numbers

We have seen that numbers in certain ranges have a specific format:

(02x) xxxx xxxx - with an eight-digit local number (created by the Big Number Change in 2000)

(011x) xxx xxxx - with a seven-digit local number (created by PhONEday in 1995)

(01x1) xxx xxxx - with a seven-digit local number (migrated from 0x1 on PhONEday in 1995)

At this point it should be noted that most of the remaining 01 numbers not already listed above, are formatted as:

(01xxx) xxxxxx  - with a six-digit local number. There are also a very few areas with this length area code and a five-digit local number.

In several very rural areas there are a few numbers like:

(01xx xx) xxxxx - with a five-digit local number. One area using this longer area code has a mixture of both five and four-digit local numbers. It is the only UK geographic area code with four-digit local numbers.

All of the current '01' area codes were changed to their new format on PhONEday in 1995, simply by adding an additional '1' after the initial '0' trunk code (except for Leeds, Sheffield, Nottingham, Leicester, and Bristol, which gained completely new 011x area codes and added a digit to the local number).

The Reading, London, Southampton, Portsmouth, Coventry, Northern Ireland, and Cardiff area codes added the '1' to the area code on PhONEday. A few years later those area codes changed again: Reading to 0118 in 1998, and the others to various new 02x codes in the 'Big Number Change' in 2000. At the same time as the area code change, the local number length also increased by one or two digits in all of those areas.

UK National Telephone Number Plan

UK numbers now mainly have ten digits after the zero trunk code, although a few have only nine digits. This is a quick summary of the correct format to use with each of the UK number ranges. Several other sites list the area codes in detail.

To be clear on how to interpret this, a '2+8' format number has a two-digit area code (after the 0 trunk prefix) and eight digits in the local number. A '4+6' format number has a four-digit area code (after the 0 trunk prefix) and six digits in the local number. When calling the UK from abroad, the 0 trunk prefix is instead replaced by '+44', where '+' means dial the international access code applicable in the country you are calling from, and 44 is the UK country code.

Code lists

Do be careful with your data. Indeed, in researching this article, most of the UK area code lists that I found online contain many of the errors mentioned above.

I found several that I could rely on:

Ofcom Area Code Tool

complete UK area code list with examples

from the People's Republic of Slough

list of UK charging groups (there's just a few minor typos).

International Format

So, far we have only discussed numbers written in the national format, like (01x1) xxx xxxx and (020) xxxx xxxx, and so on.

When writing UK telephone numbers in the International Format:

- DO correctly space out the country code, area code, and local number. This makes the number easy to use, whether the caller is calling from another country, or from the same country but not in the same area, or from somewhere in the same area.

- DO take note of the correct format depending on what the area code actually is: the 2x, 11x, and 1x1 area codes have a different (longer) local number format to those used in the rest of the country, as noted above.

- Do NOT include any International Access Code (as that differs depending on which country you are calling from). That is, DO write +44 for calling the UK, and do NOT write 00 44 or 011 44.

- Include only the digits that callers from abroad MUST dial. For UK numbers, do NOT include the leading zero trunk code. For an example London number, DO write +44 20 7234 3456 and do NOT write +44 (0) 20 7234 3456 and do NOT write +44 020 7234 3456. See ITU-T recommendation E.123 for more information. Of course, if it is an Italian number you are quoting, you would in that case write +39 06 456 4455 because you do still have to dial the zero when calling the number from another country.

Stick to these simple rules and both searchengines and humans will make the best use of the data that you present on the pages of your website.

Finally, by sticking to the correct formatting you're more likely to spot any typos; and, if you do make a mistake the reader might just glean enough information to understand what you meant.

It's a big job, but someone has to do it

Fixing the data contained on a large website is likely to be a lot of work. There are many different things to consider. Refer to table 2 and 3 for the details. In summary:

- Fix (02x) xxxx xxxx numbers to be in the correct format; e.g. 0207 555 7777 or 02075 557777 should be (020) 7555 7777. If the original number appears to be a digit short, then it's probably a pre-PhONEday number that instead needs a '1' adding immediately after the 0 trunk code; e.g. (0207) 444555 should probably be (01207) 444555.

- Look for numbers that should be formatted as (02x) xxxx xxxx, but which are quoted using their pre-Big Number Change area code; e.g. (01203) 224466 should be (024) 7622 4466. Likewise (0181) 555 7788 should be (020) 8555 7788.

- Look for numbers that should be formatted as (02x) xxxx xxxx, but which are quoted using their pre-PhONEday area code; e.g. (0203) 224466 should be (024) 7622 4466. Likewise (081) 555 7788 should be (020) 8555 7788.

- Fix (011x) xxx xxxx numbers to be in the correct format; e.g. 01179 335577 or 011 7933 5577 should be (0117) 933 5577.

- Look for numbers that should be formatted as (011x) xxx xxxx, but which are quoted using their old pre-PhONEday area code; e.g. (0602) 557788 should be (0115) 955 7788. Likewise (0734) 334455 (and 01734 334455 for that matter) should be (0118) 933 4455.

- Look for numbers quoted using those 'area codes that have never existed' and edit them to be the correct (011x) xxx xxxx number; e.g. 01742 556677 should be (0114) 255 6677.

- Fix (01x1) xxx xxxx numbers to be in the correct format; e.g. 01515 557799 or 015 1555 7799 should be (0151) 555 7799.

- Look for numbers that should be formatted as (01x1) xxx xxxx, but which are quoted using their old pre-PhONEday area code; e.g. (051) 345 4455 should be (0151) 345 4455.

You'll need to do this for numbers quoted in national format, and then again for those in international format. There's likely a whole range of other issues that you'll uncover. Fix 'em all!

Dodgy Data

No matter which you choose of the many different incorrect formats discussed in this article, you will always find lots of sites that are using them. Part 2 will take a look at several well-known sites and reveal the true extent of these problems.