If you are trying to track down information about a person using only their cell phone number, then Reverse Business Phone Lookup can help you find the reverse cell and phone numbers.
If you have in your possession a residential phone number but no idea that the number belongs to or what address it relates to you can use Phone Number Reverse Lookups..
Reverse Lookup By Phone Number contains a database of hundreds of millions of cell and unlisted phone numbers, complete with information about the owner.