Today, more and more people possess mobile devices. This enables them to have access to a wide range of services, but also to be contacted anytime, anywhere, which can cause discom- fort. Users should have full control on who can reach them and how, depending on their current situation: when at work, we wish a friend didn't interrupted us, but when having a family dinner, we wish a call related to work didn't occur. Even more, situation changes need to be detected in real-time, since preferences change a lot. We present in this paper an ontology-based user profile model, that allows users to have a situation-aware social network, by controlling how reachable they are for specific categories of people in a given situation.