A method for processing a call in a heterogeneous communication system that manages heterogeneous networks including a circuit switched, CS, network and an internet protocol, IP, multimedia subsystem, IMS, network, the method comprising: performing voice call continuity, VCC, service registration (201, 203) of a user equipment, UE, in the IMS network by a voice call management server at the request of the UE supporting both the CS network and the IMS network; receiving (205, 207, 209) by the voice call management server a subscribe message including a subscriber identification number from the UE by using an mobility event package, MEP, subscribe message; allocating (217, 219) by the voice call management server a transfer number needed by the UE to transfer from the IMS network to the CS network, in response to the subscribe message, and delivering the transfer number to the UE; performing (227, 229), by the voice call management server, location registration for the UE in the Circuit Switched network using the subscriber identification number; allocating by the voice call management server a routing number, IMRN, in the IMS network for a terminating call, and delivering the IMRN to the CS network, wherein the IMRN is used by a Media Gateway Control Function, MGCF, to directly contact an Interrogating Call Session Control Function, I-CSCF, of the IMS network; receiving by the voice call management server the terminating call including the IMRN from the CS network; determining a mobile station ISDN number, MSISDN, indicative of a subscriber number of a terminating UE corresponding to the IMRN based on the terminating call including the IMRN; and determining whether the terminating UE of the MSISDN is a UE of a VCC subscriber by an initial filter criteria, iFC processing; anchoring, by the voice call management server, the terminal call and delivering the terminating call to the terminating UE corresponding to the IMRN, wherein the voice call management server is a VCC application server, VCC AS. performing voice call continuity, VCC, service registration (201, 203) of a user equipment, UE, in the IMS network by a voice call management server at the request of the UE supporting both the CS network and the IMS network; receiving (205, 207, 209) by the voice call management server a subscribe message including a subscriber identification number from the UE by using an mobility event package, MEP, subscribe message; allocating (217, 219) by the voice call management server a transfer number needed by the UE to transfer from the IMS network to the CS network, in response to the subscribe message, and delivering the transfer number to the UE; performing (227, 229), by the voice call management server, location registration for the UE in the Circuit Switched network using the subscriber identification number; allocating by the voice call management server a routing number, IMRN, in the IMS network for a terminating call, and delivering the IMRN to the CS network, wherein the IMRN is used by a Media Gateway Control Function, MGCF, to directly contact an Interrogating Call Session Control Function, I-CSCF, of the IMS network; receiving by the voice call management server the terminating call including the IMRN from the CS network; determining a mobile station ISDN number, MSISDN, indicative of a subscriber number of a terminating UE corresponding to the IMRN based on the terminating call including the IMRN; and determining whether the terminating UE of the MSISDN is a UE of a VCC subscriber by an initial filter criteria, iFC processing; anchoring, by the voice call management server, the terminal call and delivering the terminating call to the terminating UE corresponding to the IMRN, wherein the voice call management server is a VCC application server, VCC AS.