This chapter approaches sustained car conversations across mobile phones and in-car phone resources as a session management problem. Addressing this problem, the chapter outlines a session management model for user-controlled media switches during ongoing phone conversations. The model makes a distinction between the user and the infrastructure levels of session management. To illustrate and validate the rationale of the model, the chapter presents an in-car mobile phone hands-free system, SeamlessTalk, developed to support sustained car conversations. The user-controlled session management model contributes to current research on session management by addressing the explicit/implicit session management dichotomy in multiple media situations.