Modem signaling using a multitone prefix over a voice channel of a wireless communication system

A method of communicating data between a vehicle and call center via a voice channel of a wireless communication system, comprising the steps of:

• establishing a voice channel connection between a vehicle telematics unit and call center via a wireless cellular network;
• generating a modem signaling carrier comprising a prefix followed by a single frequency tone, wherein the prefix comprises a speech component or a speech-like audio signal having multiple spectral components in the audio frequency range that each vary over time in amplitude, frequency, or both;
• sending the modem signaling carrier over the voice channel connection using an Enhanced Variable Rate Codec B (EVRC-B) vocoder;
• establishing a data communication session over the voice channel connection in response to the modem signaling carrier;
• and thereafter
• carrying out data communications between the vehicle telematics unit and call center during the data communication session.