Kelvyn Taylor, a columnist for both business rag IT Week and consumer mag PCW, predicts increasing problems as more auto makers put Bluetooth capability into their cars and promise buyers that they will be able to make calls by prodding the buttons on their steering wheels. He tells a tale of woe involving a Seat Altea, a Bluetooth phone, and a very disgruntled customer:

I think anyone who's used Bluetooth can guess what happens next. His handset, an I-Mate Jam smartphone, refuses to connect to the system. Further investigation revealed that Seat has a list of a couple of dozen compatible phones, and of course this doesn't list the [I-Mate]. In fact only eight of the listed models offer full functionality - the rest only offer audio functions.
What's even worse is that he can't even use a separate Bluetooth headset because every time he gets in the car the phone tries fruitlessly to negotiate a connection with the in-car system.

As Taylor goes on to speculate, it makes you wonder what would happen if, stuck in traffic in your Seat Altea, you happened to find yourself next to someone who does have a compatible phone...
Buyers would be well advised to pore over the small print when sizing up Bluetooth compatible cars. And be prepared to buy a new phone.