The notion of context has become very important in computer science, especially when users are highly mobile. In a short period of time the environment changes; communication networks can become available or unavailable, user communities can appear or disappear, etc. The work presented in this paper focuses on the transportation domain and more particularly on applications which accompany and assist the user in transportation activities (e.g., driving, visiting a city, etc.) through the use of ad hoc social networks. We present a case study related to the VESPA system, designed to help drivers by providing them with diverse information (e.g., traffic information, available parking spaces, etc.); we show how the framework we propose can help the system deal with context issues. In the last part, we analyze different mechanisms of changing application behavior through the use of services, an important step towards making our devices reactive to new situations