WhoCallsMe is a user-supplied database of phone numbers, whereas Argali White and Yellow provides software for phone-number searching. Truecaller has an online directory and a mobile app for finding the ID of a caller.
Looking for the owner of a telephone number is called reversed phone lookup. Reversed phone lookup should always be free because, according to About.com, websites that offer these services have access to exactly the same information on the Web that you have, and if you can't find the number, they can't find it either. Phone numbers are impossible to track down if kept private by their owners.