The invention provides a method of selecting a modem carrier type for data transmission over a wireless communication system. An incoming call is received from a mobile vehicle and then an initial carrier tone is sent to a mobile vehicle in response to the incoming call. A modem response signal is received from a vehicle modem in response to the initial carrier tone. The modem response signal is determined to be either an analog modem response signal or a digital modem response signal, and then the call is connected to either the analog modem or digital modem based on the modem response signal determination.