In one aspect, a communication system allows telephone users to roam between cellular and broadband domains and obtain equivalent level of service and features in the broadband network as in the cellular network. For example, such users can make use of Push-To Talk service, as well as continuous telephone call service, independent of which domain they are connected through. In another aspect, users can pass messages, including voice messages, or establish two-way voice communication between disparate push-to-talk (PTT) or messaging and/or voice systems. For example, a user on a cellular network using a PTT service is able to communicate with a user on a data network using an IM service. In addition, information is passed between the systems to provide coordinated presence information for users. For example, a user can have presence information in multiple networks enabling users form different networks to communication with that user.