Heterogeneous communication system and method for processing call in the same system

The present invention relates to a speech call processing method in a communication system and the system to operate a heterogeneous network. The present invention when the terminal requests a call setup to voice call sent to the management server of the IMS network, the subscription message comprising a subscriber identification number, wherein the voice call management server, registering the terminal in the IMS network, the subscriber identification number using performs the location registration to the home location register of the CS network. Two kinds of communication systems, CS network, IMS network, VCC AS