Abstract: Methods of IP to IP handover for VoIP calls are disclosed. Handover can occur using UDP in connectionless mode to switch networks, a hybrid approach including establishing both a TCP session and a UDP session and handing off using the UDP session, utilizing a network SIP proxy to maintain connection with the IMS server while the mobile device switches networks connecting the mobile device to the SIP proxy, using a modified Connection Manager that permits multiple IP connections simultaneously, and connecting via an on-device virtual network to an on-device router which reroutes calls to the appropriate network are detailed.

Abstract: A method of making Voice over Internet Protocol (VoIP) calls, legacy circuit calls, sending/receiving Short Message Service (SMS) over Long Term Evolution (LTE) modem or a legacy modem on a mobile terminal with both kinds of modems, and providing all legacy modem functions is disclosed. In addition, methods for dynamic selection of radio in a mobile terminal capable of Rich Communications Services (RCS) capabilities, and a method for redirecting RCS traffic to an alternate network interface is also disclosed. Methods for Session Initiation Protocol module (SIP) stack functions to be distributed across different processors on a mobile terminal, and directed to different network interfaces is disclosed. Methods of adding video calling and RCS functions without encountering the dual registration problem are also disclosed.