New challenging deployment scenarios are accommodating limited and heterogeneous portable devices that roam in wired-wireless best-effort networks with session maintenance and continuity requirements. In particular, continuous services, e.g., multimedia streaming, should not experience any interruption while clients roam between different wireless access localities during service provisioning. The paper describes how to exploit the Session Initiation Protocol (SIP) to build a middleware for session continuity, also by integrating with our novel context-aware SIP notification package. In particular, the proposed middleware makes use of SIP notifications to update session information and to proactively activate session reconfiguration for roaming clients. Experimental results show that, notwithstanding the portable Java-based implementation, our SIP-based solution is feasible in most common wireless Internet deployment scenarios and achieves good scalability.