If you have in your possession a phone number but you don't know who it belongs to you can use a reverse cell phone directory to track down information on the owner. There are different search methods you can use when performing a reverse yellow pages lookup.
Technology has advanced and has given us ways to use cell phone lookups to find phone numbers of friends, family, or other people we may want to call. Have you ever met somebody and gotten their phone number, but couldn't remember their name or you wanted to look them up? It wasn't that many years ago when even finding what number belongs to what cell phone company was impossible.
You can also do an area code search where you enter in the area code. Your information is being bought, sold, and shared between companies and government agencies every day, all the time. Sometimes you won't find a number this way, but it is usually a great first step in your search, and might even be the only one you need to try.
As always your searches are guaranteed legal and confidential. You can use this system to find out who is calling your phone.