An apparatus and method for seamlessly providing voice and data services to a user through an access terminal in a mobile communication system including a heterogeneous service & mobility gateway (HSMG) for an interworking service between a circuit network and a packet network, and various access networks overlapping each other. The access terminal notifies the HSMG that a voice call is received, if the access terminal that accessed a packet network receives a voice call. The HSMG sends a direction request to a circuit network upon receiving the notification indicating that the voice call is received. The access terminal directs to the circuit network and registers a new location upon receiving the direction request. The HSMG sets up an incoming voice call to the access terminal after the registration of a new location.