Abstract: A method for configuring voice and data communication over a voice channel of a wireless telecommunications network that includes an onboard vehicle communications system, a cell tower, a base station, a Public Switched Telephone Network (PSTN) and a remote call center. Initially, a component on the network side, such as a network vocoder incorporated within a base station, selects a data rate during configuration of the voice channel. Thereafter, an onboard vocoder incorporated within a chipset of the onboard vehicle communications system sends a service option control message to the network vocoder requesting a higher data rate for the subsequent voice and data transmissions. A similar process occurs during a handoff that involves a change of network vocoders.