You can use rLookup to find out who is calling you by searching for the caller ID of the phone number you have on your phone. This is the most useful app to find out who is calling you since it can work with both landline and cell phone numbers.

This app can also work with the number you have listed on your profile on a social network. If you have a number listed on your profile, you can use rLookup to find out who is calling you by searching for the caller ID of that number.

This app is very useful since it can work with numbers issued by several carriers such as AT&T, Verizon, T-Mobile, Metro, Optimum Mobile, and Rogers.