This is based on SIP protocol .
Make cheap international calls by subscribing and enjoy the crystal clear quality voice .
Also this Dialer has built-in security module which can encrypt the voice packets and allows you to call from anywhere even from VOIP blocked areas and behind firewalls .
Brand pin and voip account are provided by the service provider . You can not use this app without a voip account.
This is based on sipsimple find the source code of the same here https://github.com/balusreekanth/Android_SipDialer