Developer's DescriptionBy WESY S.A.SCalls SIP VoIP ATT is a very useful mobile application that enables users to make VoIP calls from their mobile devices to anywhere around the...Calls SIP VoIP ATT is a very useful mobile application that enables users to make VoIP calls from their mobile devices to anywhere around the world. Call connections are established on the end party mobile devices even though they dont have this application installed and that's what makes it so special.Users can have a great time exploring different call features of the app and get benefited in the form of seamless VoIP calling even in low bandwidth areas.