I've got the
AutoPilot from Griffin, and I haven't seen any issues with it. Anyone with one of those and have concerns shouldn't worry; it'll continue to work.
Granted, it interfaces with the iPhone via the dock connector, but eventually goes into the car's audio system via the auxiliary jack, so the USB connection is probably what the issue is with other audio systems.
I've also noticed the "This accessory isn't meant for your device" message doesn't give you the choice of going into Airplane Mode; it just reminds you that you'll probably get interference.