1. A method to operate an event notification system comprising an event server and a subscriber unit, comprising: associating with a particular event subscription an “available” event template subscription; sending an initial notify message to the subscriber unit with a current availability of an event state of the event subscription; and for the duration of the particular event subscription, upon detecting a change in the availability of the event state sending an “available” event template notification to the subscriber unit from the event server for informing the subscriber unit of the change in the availability of the event state.