Starting from a context-aware phonebook application, which allows users to see their contacts' situation, we introduce a collaborative context experience system. Users independently create notification rules, describing phonebook-based contextual situations for which they wish to receive notifications. The collaborative system gathers such rules from all users, and identifies important ones, that is, frequently declared ones. These rules are then processed to allow for generalization, and provided to users who can encounter a similar contextual situation. Similarities for this collaborative knowledge sharing mechanism are processed by applying semantic technology.