A communication system includes User Equipment (111), Radio Access Network (RAN) (121), a packet-switched domain (131), an IP Multimedia Subsystem (IMS) (141), a circuit-switched domain (151), a Domain Name System (DNS) (165), a Charging Gateway Function (CGF) (134), an EIR (135), a Transport Signaling Gateway (T-SGW) (146), and a Roaming Signaling Gateway (R-SGW) (147). The CS domain (151) includes an interworking Mobile Switching Center (iMSC) (201). The iMSC (201) translates the CS domain registration, call control, feature control, and feature invocation procedures associated with the access technology to standard SIP procedures. The media gateway (MGW) (173) under the control of the iMSC (201) converts the air interface media flow into a packet stream that is managed by SIP procedures within the IMS (141). The iMSC (201) thereby allows for interworking between circuit-switched and packet-switched domains for call terminations.