According to www.about.com, while mobile phone numbers are notoriously tricky to look up, there are a couple of tricks you can try. Here are a few:
If you want to Track down someone’s mobile phone number,it can be difficult, if not impossible. But it does not mean it is not achievable.
Use search engine
If you have a phone number, enter it into your favourite search engine and see what comes up. If the mobile phone number you are looking for has ever been entered somewhere on the Web – a blog, a public job profile – it will show up and you’ll be able to identify the owner.
Use social media
There are literally hundreds of millions of people who are active on various social networking sites all over the world. Many people share their phone numbers on these sites. Simply type the person’s name into the site’s search function and see what comes back.
For instance, Facebook is a great source for tracking people down. Simply go to the person’s profile, check basic info, check contact information. Note that you can only see a number that the owner makes visible. If it is marked as private, you will not be able to see it.
Search across websites for the same username
Usernames, individual identification codes/names of people accessing a computer, network, or website, are useful tracking tools for phone numbers. Since many people use the same username across multiple sites, you can sometimes get their phone numbers by simply typing that username into your favourite search engine. If the person has entered in their phone number somewhere on the Web underneath their username, it will come up in a search engine query.
Source: Punch News\Rayoonline