With the near ubiquity of mobile phones, people are reachable almost anywhere and at any time. The conve- nience this provides for people to more effectively combine different aspects of their lives has the consequence of an in- creased 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 mo- bile 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 mo- bile devices to enable users to manage calls, based on the caller and caller?s group, the time and day, and their ac- tivity. The system uses a new rule-based technique, Priori- tized Ripple Down Rules, which gives the user a high level of confidence in the system?s behaviour.