A method of using a converged core network service, a universal control entity (UCE), and a converged core network system. The method includes establishing, by a terminal, a signaling connection with a converged core network supporting a plurality of access networks through a first access network, and after establishing the signaling connection, using, by the terminal, a data service through a second access network by reusing at least one of authentication information authenticated and resource information allocated upon establishing the signaling connection through the first access network.