With the near ubiquity of mobile phones, people are reachable almost anywhere and at any time. The convenience this provides for people to more effectively combine different aspects of their lives has the consequence of an increased blurring of boundaries, for example between work and home. Thus, as one sphere impinges upon others, we see a need for people to limit their interactions on the mobile phone, to control (within socially acceptable bounds), when they are reachable and by whom. In this paper, we present a call handling personal assistant that runs on mobile devices to enable users to manage calls, based on the caller and caller’s group, the time and day, and their activity. The system uses a new rule-based technique, Prioritized Ripple Down Rules, which gives the user a high level of confidence in the system’s behaviour.