A method of implementing push-to-talk (PTT) communication between network phone clients utilizing Session Initiation Protocol (SIP) Voice over Internet Protocol (VoIP) and multicast RTP, includes pushing a "Talk" button on a talking client to generate a PTT invitation message (via SIP INVITE or MESSAGE), transmitting the PTT invitation message from the talking client to a SIP server, transmitting the PTT invitation message from the SIP server to a PTT server, consulting a group list stored on the PTT server to identify a plurality of receiving clients associated with the talking client, sending the PTT invitation message from the PTT server to the plurality of receiving clients, the PTT server receiving acknowledgement of the PTT invitation message from the plurality of receiving clients. The PTT server arbitrates the token-requests of the clients, translates a unicast-to-multicast RTP of token-request and talk-burst packets, and then broadcasts to all clients.