Phone number normalization: Any pre-existing libraries?

Question

I have a system which is using phone numbers as unique identifiers. For this reason, I want to format all phone numbers as they come in using a normalized format. Because I have no control over my source data, I need to parse out these numbers myself and format them before adding them to my DB.

I'm about to write a parser that can read phone numbers in and output a normalized phone format, but before I do I was wondering if anyone knew of any pre-existing libraries I could use to format phone numbers.

If there are no pre-existing libraries out there, what things should I be keeping in mind when creating this feature that may not be obvious?

Although my system is only dealing with US numbers right now, I plan to try to include support for international numbers just in case since there is a chance it will be needed.

Edit I forgot to mention I'm using C#.NET 2.0.

Answer 1

Just strip out any non-digits, possibly using a RegEx: [^\d]

The only exception might be if you want to handle extensions, to distinguish a number without an area code but with a 3 digit extension, or if you need to handle international numbers.

Answer 2

I'm currently involved in the OpenMoko project, which is developing a completely open source cell phone (including hardware). There has been a lot of trouble around normalizing phone numbers. I don't know if anyone has come up with a good solution yet. The biggest problem seems to be with US phone numbers, since sometimes they come in with a 1 on the front and sometimes not. Depending on what you have stored in your contacts list, it may or may not display the caller ID info correctly. I'd recommend stripping off the 1 on the phone number (though I'd expect most people wouldn't enter it in the first place). You may also need to look for a plus sign or country code on the front of international numbers.

You can check around the OpenMoko website, mailing list, and source control to see if they've solved this bug yet.

Answer 3

perl and rails examples

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http://validates-as-phone.googlecode.com/svn/trunk/README

http://www.perlmonks.org/?node_id=159645