VoipTiger is a VOIP application and makes calls over the Internet at even more competitive rates than with CallTiger. However, it requires a stable internet connection. CallTiger, on the other hand, is a callback application that uses no VOIP. It works 100% over the mobile network by setting up two calls: 1 call to your mobile number and another call to your contact. With VoipTiger you set up only 1 call over Internet.