Ip multimedia subsystem for supprting voice service and call setup method thereof

An IMS(IP Multimedia Subsystem) for supporting a voice service between different networks and its call setup method are provided to allow providers of services such as the wireless Internet or WCDMA to provide a voice service. A CSCF(Call Session Control Function)(111) processes a call and a session of networks by using the SIP(Session Initiation Protocol). An HSS(Home Subscriber Server)(140) stores an integrated profile of data service and voice service subscribers, and transmits the profile to the CSCF(111). An MGCF(Media Gateway Control Function)(121) allocates resources and performs a signaling processing operation when a call is established between networks. An MGW(Media Gateway)(123) converts traffic between networks under control of the MGCF(121).