In this paper we tackle the mobility issue in IP Multimedia Subsystem (IMS). Although IMS was designed to integrate different access networks, mobility management among these networks is still unresolved. We propose a novel hybrid mobility management scheme, based on tight cooperation between fast handovers for mobile IPv6 (FMIPv6) and session initiation protocol (SIP) to ensure an uninterrupted real-time service. Moreover, the new Media Independent Handover (MIH) service is integrated into IMS architecture in order to perform intelligent and accurate horizontal and vertical handovers. We investigate two handover cases: selected handover and forced handover. Selected handover takes place when user equipment (UE) is connected to the network via two interfaces at the same time and decides to upgrade the quality of its connection following a given criterion (i.e. cost, bandwidth…etc) without having any difficulty in the previous link. As far as forced handover is concerned, it occurs when the signal reaches a critical level and UE is forced to make a handover in order to maintain the ongoing communication. This case is managed in two phases. The first one or the fast phase is handled by FMIPv6 protocol to preserve as soon as possible packets of the ongoing communication. The second one or the slow phase is handled by SIP protocol to optimize packet delivery route. By doing so, we exploit the benefits of both network layer and application mobility protocols to ensure a continuous session over the two networks without imposing new elements to the network. Through a comparison with other mobility mechanisms, we show in the analytic analysis that our hybrid scheme presents better results in terms of handover latency and packet loss