Wikipedia:Call.center (application)

call.center is a softphone for OS X, Windows, Android and iOS. It uses Session Initiation Protocol for communication. call.center is distributed as free software. call.center is a standalone softphone and not a VoIP service. A VoIP service or subscription is required to make or receive calls.

Audio codecs

 * OPUS
 * G.711 family codec (PCMA, PCMU);
 * GSM;