The context of our work is mobile multi-homed terminals in a heterogeneous environment. We propose a solution for seamless terminal mobility in an intra-domain context. We combine a multi-homing protocol (SHIM6), which ensures seamless network change, with the IMS architecture, which allows the establishment of multimedia session with Quality of Service. Our proposal allows a mobile terminal to change its access network seamlessly, without any application disruption. To achieve this, we implement a Proxy-SIP inside the terminal to manage session establishment. The proposed scheme can manage access network change in two modes: reactive and proactive. A testbed allowed us to show the feasibility of our approach and the gain obtained by considerably reducing the handover delay and, thus, data loss.