1. A system for providing role-based Presentity availability information to a Watcher, comprising: at least one Presentity User Agent for issuing a request to register a Presentity in at least one of a plurality of roles, and for generating context messages relating to changes in context of said Presentity; at least one Watcher User Agent for issuing a role-based subscription request for said availability information; a Presence Service for maintaining role-based Watcher subscriptions and issuing availability messages in response to generation of said context messages; and a Role Manager for (i) receiving each request to register a Presentity in said at least one of said plurality of roles and in response managing Presentity registration in said plurality of roles, and (ii) receiving each said role-based subscription request, and in response managing each role-based Watcher subscription to said availability information within said Presence Service.