There are probably head units capable of this, by mounting your phone as a storage device (same way you're mount it while hooked up to a PC)... But I'm pretty sure the vast majority of stock head units (even on luxury cars) won't do it... Ford's Sync might be the exception. Either way, Bluetooth is a far simpler solution and the quality is acceptable, not to mention the freedom of just getting in your car and hitting play on the steering wheel to play tunes from your phone, even if it's still in your pocket/bag.
The vast majority of recent head units that I've seen let you do music payback as well as calls over Bluetooth and they handle both seamlessly. You can even get 12V powered kits that plug into your aux unit and replicate the same functionality, usually minus steering wheel controls, though if you can track down the Kensington Liquid Aux I highly recommend it (the remote is awesome). If you need to charge the phone you can just plug in a standard charger (the Kensington unit has a charging port too btw, so it doesn't take over your 12V port).