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The recent advances in wireless client devices and the crucial role of multimedia communications in our society have motivated relevant standardization efforts, such as the IP multimedia subsystem, to support session control, mobility, and interoperability in all-IP next-generation networks. IMS has already driven the design of commercial mobile multimedia, but exhibits limited support for service continuity during handoffs. In particular, it omits advanced techniques to reduce/eliminate handoff delays, especially during vertical handoffs (i.e., change of the wireless technology employed by a client to access the wired Internet, e.g., from UMTS to WiFi). We propose an original solution for session continuity based on the primary design guideline of cleanly and effectively separating the signaling plane (for session reconfiguration via SIP) from the media delivery plane (data transmission and related handoff management operations). Our optimized handoff management techniques exploit terminal-based decentralized predictions to minimize service-level handoff delays. Different from other recent related work, our proposal fully complies with the standard IMS infrastructure and works at the application level. The reported experimental results point out that our solution, available as an open source tool for the IMS community, reduces playout interruption times relevantly by introducing a limited and scalable signaling overhead.