It is difficult to know who is calling you if you do not have a caller ID and if you have one, there are callers that do not show their name and phone nos. so; it is hard for you to find out who is really calling you. If you are seeking a site to find out who is calling you, this National Phone Registry might be the one that you are looking for as they have powerful tools that you will be able to find unlisted phone nos., prank calls and others which are hard to find of the owner information. To know more about it, you can check their site.