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I would like to find a tool/library that can take user-entered free format telephone numbers entered through a web site and parse them into a number suitable for calling from a given country.

This is not quite as simple as it may at first sound. The website allows people all around the world to enter their number in any way they choose, so many people enter national numbers (a country is also provided in another field). Some people enter the international number in "correct" formats (with the "+"), some people enter it slightly less correctly, using their country's international prefix.

I would like to tell the library/tool the country that I'm dialling from, and the free-format telephone number and optionally the country that this corresponds to (as this will help generate the international code if not entered), and it use known patterns to best-guess the number that will work in my calling country

So, for example, when calling from the US to a UK number:

+44 (0) 1225-344567 => 011441225344567

Or when calling from the UK to a US number:

(613) 4562342 => 0016134562342

Anyone know of any (ideally .NET Framework-friendly) solutions that will avoid me undoubtedly re-inventing the wheel

Kara
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Kram
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    Such a library sounds like it would be very niche. Not to mention, there aren't any standard rules. Even in the same country, there can be different number formats if you're calling to/from a cellphone to a land-line! The best solution for international telephone numbers is, unfortunately, a free form textbox. – Mike Caron Jun 27 '11 at 15:10
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    Thanks. We already have the free-format box. I've linked this into our telephone system so that people can call customers without having to (often incorrectly) enter the number into the phone. However, I've had to implement some custom code to massage the numbers as in the examples above... and this is made harder by us having both US and UK offices, and it occurred to me that there may be some code already out there to do this (even if we need to pay for it) - I've got bigger fish to fry ;) – Kram Jun 27 '11 at 17:39
  • http://stackoverflow.com/q/187216/469210 appears similar. – borrible Jun 28 '11 at 11:01
  • I've got a C# library on [GitHub](https://github.com/AgentTy/General) that offers this exact functionality. It uses an embedded XML database of countries and area codes within each country to understand the context of any phone number, and how to call any one number from any other number. – Ty H. Sep 06 '15 at 02:55

5 Answers5

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I've implemented just this, Mark. I work for a wireless carrier and have an international SMS sending application. I am not aware of any third party libraries that implement these rules. As mentioned above, one cannot just deal with random input as the phone number formats vary among countries. Some countries such as Germany have variable length area codes and phone numbers. If they don't put the country code in there you are sunk. However, in my case I can assume if it's missing a country code it's a USA phone number. The results of my filter have proven to be very accurate with the users and input I've had.

One can make some assumptions, and by knowing the target audience, logging the inputs, and analyzing, one can get things dialed in. My first implementation was for a "white label" web app that is used for testing by various people around the world. I rapidly found that most foreign people have their act together and are used to the quasi-standard + format. It's usually Americans entering phone numbers that are most confused. Europeans are very used to international dialing.

First rule is to strip out everything but digits and a leading '+'.

If the resulting number has fewer than 8 digits, it's junk, provide user error.

If the resulting number starts with a '+' assume it is the standard format and that the next 2-6 digits represent the "country code". Figure out the country code then process the remaining digits according to the rules for that country.

If the number starts with 0, assume someone put in an international access prefix, and strip off leading 0's and 1's, then: if the remaining number is 10 digits, assume it was a USA number entered by an American, and handle accordingly. If the remaining number is not 10 digits, but at least 8, assume the first 2-6 digits are a country code, lookup the country code, and process according to that country's rules.

If the number starts with a 1, and it is 11 digits total, assume it is a USA (or Caribbean Island) number, and process accordingly.

IF the number starts with a 1 and is not 11 digits total, strip the leading 1s, see if there are at least 8 digits left, and assume the remaining leading 2 to 6 digits are a country code and process per the country rules.

Finally, with the number not leading with +, 0, or 1, and being at least 8 digits, assume it is in the standard notation without the +, that is country code first, use the first 2 to 6 digits as the country code and process according to that country's rules.

The trick in all of this is to have a mapping of all the world's country codes, and the numbering plan information for each country. I have that map, and the rules for many countries. If you would like this information I'd be happy to share, along with some C# code that figures out which country. Message me.

A huge help in this is to post back the name of the country your software is guessing to the user. They will understand rapidly if they are trying to enter a German phone number and your software asks them if they are trying to dial Guam!

Christo
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  • Contact you how, Christo? (I want your implementation, it's more complete than mine) – Peter Wone Jun 28 '11 at 13:29
  • @Peter He said "I work for a wireless carrier" so this is day-job stuff - very likely it belongs to his employer and he can't give it to you. (without begging them to open-source it) – Rup Jun 28 '11 at 13:38
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Yes: Google's common Java, C++ and Javascript library for parsing, formatting, storing and validating international phone numbers has now been ported to C#:

https://github.com/erezak/libphonenumber-csharp

Good Luck!

Shimmy Weitzhandler
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LaTisha
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  • From what I can tell this is indeed the best option... however really want it in .Net also... just came across this, which claims to do the job: http://blog.thekieners.com/2011/06/06/using-googles-libphonenumber-in-microsoft-net-with-c/ – Kram Jul 28 '11 at 08:34
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Google's library library for parsing, formatting, storing and validating international phone numbers has now been ported to C#.

https://github.com/erezak/libphonenumber-csharp

Shimmy Weitzhandler
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Aaron Gray
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No, there isn't :) There are very few rules that govern telephone numbers between nations. Some countries even have multiple representations.

The UK for instance has variable sized area codes eg:

  • 0121 = Birmingham
  • 01223 = Cambridge
IanNorton
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There is a "standard" to format international ( and national ) phone numbers. They look like this: +31 42 123 4567 (+country prefix number callthrough). Example taken from Wikipedia. Though you shouldn't expect anyone to enter it that way. In my experience users most likely will stick to the format they're used to.

I do not know of any library that will convert between all ( mostly local ) representations to that mentioned by me or any other format.

Sascha
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