The mobile phone, an object of negotiation between parents and teenagers, frees users from certain constraints yet creates others. It preserves young people's individuality and creates a sphere of autonomy, but also binds generations. Nurturing every aspect of the social link, it is both an element of the subject's culture and a tool for learning to manage financial and relational constraints. The mobile phone can thus facilitate autonomy and hinder it. The author talks of "paradoxical privacy" with regard to these complex mediations in which it operates.