The IP multimedia subsystem (IMS) is a service control overlay standardized by the 3GPP. The IMS is based on session initiation protocol (SIP) to establish, modify, and terminate the sessions. It provides a clean separation between services, signaling, and media with the potential to enable control and management of services over multiple transport technologies. In the scope of fixed-mobile convergence, this paper is dedicated to presenting a review of how cable networks can be integrated into IMS technology to achieve 3G-cable horizontal convergence. Cable networks, as one of the major fixed broadband access technologies with PacketCable architecture, are able to provide broadband internet access and VoIP in addition to cable TV. In this article, we review the evolution in PacketCable architecture to take up IMS. In this way, we consider the standardization and research activities to address this integration. We review some important challenges such as SIP protocol compatibility, defining unique user profile, required enhancement in authentication process, QoS and charging system