Facebook has a good database of phone numbers of people who has been signed up. Any person who is going to create an FB account should have a phone number. Facebook allows to search people through this number. Normally if you typed phone number on the find friend bar on facebook it normally search for the person with that number. But it wont works sometimes. Following is a trick for getting around this.
http://m.facebook.com/search/?query=123456789
Here is the magic link for check a person from his number. In this link instead of 123456789 put the phone number with area code.
