With 3G, 4G, etc.. IMS – IP Multimedia – is implemented and supported. VoLTE, ViLTE, etc.. uses the IMS layer.
I am assuming that your application is based on GSMA’s RCS – Rich Communication Suite. SIP / Diameter is used.
The Network will support Gateways that can act as a converted for 2G IN (Intelligent Network) protocols.
Also look at WebRTC – Real Time Control.
VBR/ Wallis Dudhnath