Each of a number of gateway network radios operates with a transmission protocol of an associated one of plural incompatible communication networks. Each network radio has an audio terminal for producing first audio signals detected from transmissions of user radios in its associated network, and a microphone terminal for receiving second audio signals for transmission to the user radios. A voice bridging gateway server has multiple ports each corresponding to one of the networks for coupling to the network radio associated with the one network. Each port receives the first audio signals from the audio terminal of the associated network radio, and produces the second audio signals for applying to the microphone terminal of the network radio. The server implements a private branch exchange application whereby user radios in a given communication network can be voice bridged with user radios in a selected one or more of the other networks.