A service system (1) comprises a service core (1(f)) and an interface (1(d)) for interfacing with instant messaging clients (10). The service core (1(f)) controls interfacing with an instant messaging client to provide an interactive service according to an application and involving routing of multimedia content to the client (10). The system (1) is modal, dynamically interacting with a client to provide a desired service in a current mode for a user, the mode being an application state and associated group of user interactions. A mode database manager 1(a) maintains a persistent record of the mode of a service for a user. The service core (1(f)) interfaces with the mode database manager (1(a)) to allow a mode to persist through at least two instant messaging sessions involving interaction. A directory manager (1(b)) manages registered instant messaging users, and the mode database manager (1(a)) maintains mode status only for registered users. The system also comprises a presence compositor (1(c)) for publishing modes of services as users of a presence network, and some users are avatars displayed on client display screens and representing modes. A mail store manager (1(e)) is instructed by the service core (1(f)) to perform messaging operations according to service mode changes.