Abstract: "Dispatch overdialing" permits radio transceivers already communicating via a repeater with other transceivers in a trunked radio communications system to call additional radio transceivers onto the communications channel in use. A radio transceiver in a first group may "dispatch overdial" another radio transceiver in a different group by transmitting a dispatch overdial begin signal to the repeater. The repeater mutes all audio communications on the channel, and the radio transceiver then transmits a sequence of identifying signals which are identical to those used to establish communications initially. The radio transceiver then transmits a further sequence of identifying signals which identify a further radio transceiver (or group of transceivers) to be called onto the channel. If the first sequence of identifying signals matches the signals which were used to establish communications initially, the repeater initiates handshake signalling to call the further transceiver(s) onto the channel.