A method in a communication system, the system comprising a first entity maintaining registration information from a plurality of users and a second entity maintaining information associated with said plurality of users, wherein said second entity information is dependent on the registration information. The method comprises sending a subscribe message for an event from the second entity to the first entity, wherein the event is a change in the registration information of at least one of the plurality of users at the first entity; receiving at the first entity a register message from at least one user, said message changing the registration information of said at least one user; sending a notification from the first entity to the second entity in response to the register message, wherein the notification includes information associated with said at least one user.