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.