An exemplary gateway apparatus provides push-to-talk (PTT) communications between users in one network with users in another network where the networks utilize different communication protocols. It includes two protocol modules that interface with the two networks, respectively. The protocol modules are capable of receiving and transmitting messages compatible with the communication protocols used by the associated networks. An interoperability module, connected between the two modules, converts PTT control messages received from one of the networks into PTT control messages compatible with and transmitted to the other network. The PTT control messages received from the one network have a protocol that differs from the protocol of the PTT control messages transmitted to the other network.