Roaming service system for gsm service subscriber in cdma service area, and method for registering locations and transmitting and receiving signals and short messages using the system

The roaming service system comprises an international roaming gateway system (300) connected between a CDMA system (100) and a GSM system (200) providing a roaming service in the CDMA service area for a GSM subscriber having a GSM SIM card installed in his CDMA terminal (150). Methods using the roaming service system are provided to enable a roaming GSM subscriber to register the location , to originate and receive calls and to send and receiving short messages (SMS) in the CDMA service area. Futhermore an authentication center (260) is connected to a GSM network (210) to authenticate GSM terminals (250) and roaming GSM subscribers each having a GSM SIM card installed in their CDMA terminals (150). The CDMA system (100) supports either the international mobile subscriber identity (IMSI) stored in the GSM SIM card or a temporary mobile identity (TMIN) to register the location of the roaming GSM service subscriber.