I've had Bluetooth for the phone to the car sound system in the last ten or so cars. It's dead simple to use, no effort required - it switches over to "car" if I'm in the car with the ignition on, with no beeps or burps. It's Keef-proof!
The other "plus" is that the memsahib knows how to use it while I'm driving - press "Phone" button, enter the number to call on the radio keypad, press the green button, talk. Press the red button and the phone disconnects and the iPod/CD/radio comes back on.
Phone rings while driving? Press the button on the end of the indicator stalk, talk.