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 800 Phone Number Reverse Lookup.
If you are trying to track down information about a person using only their cell phone number, then Business Reverse Lookup can help you find the reverse cell and phone numbers.
Phone Number Reverse Address contains a database of hundreds of millions of cell and unlisted phone numbers, complete with information about the owner.