I had it connected through ir on the empeg once here
I guess that if you can connect the phone directly to the serial port, you could just start sending AT-commands to the serial port.
Let me know if you know how to tap the serial line from the car-kit cradle. I could also buy a cheap card-phone with an internal modem and install it somewhere in the dash. People could SMS me and the message would pop up on the display... hmmm...

Frank van Gestel