A method and system is provided for peer-to-peer communication among a plurality of sites in a land mobile radio (LMR) system. The sites are interconnected by a data network, such as an IP network. When a site, referred to as the initiating site, intends to communicate with other sites, the initiating site transmits a call request message. The call request message is multicast over the data network to the intended recipients. The initiating site receives an acknowledgement message from the other sites confirming their willingness to communicate with the initiating site. The initiating site then sends a voice message, via multicasting, to the other sites interested in the call.