The Callback feature makes it possible to talk comfortably even with a poor quality of the Internet connection. This feature will help you save the Internet traffic without any loss in quality of communication.
Callback technology is unique because an initiated call is in fact an incoming call both for you and the receiving party. Consequently, the quality of the Internet connection does not affect the quality of the talk. This is especially important while roaming or paired with a tourist SIM, when every megabyte counts.