Patent ID: 8001181

Claim:
A communication system comprising: a first wireless mobile terminal for operating on a first wireless carrier network to communicate using a push-to-talk (PTT) mode; a second wireless mobile terminal for operating on a second wireless carrier network different than the first wireless carrier network to communicate using the PTT mode; a networked computer for operating on a packet network to communicate using the PTT mode; and a message server operating on the packet network, and residing outside of the first and second wireless carrier networks, to exchange PTT messages among the first wireless mobile terminal, the second wireless mobile terminal and the networked computer; said message server is configured to store a user identification (ID) and user password for logging into an external instant messaging (IM) system, log into the external IM system as a proxy on behalf of a PTT message sender using the stored user ID and user password, determine whether an intended recipient of a PTT message is an IM client located within the external IM system, and forward the PTT message using the message sender's external IM service account.