Scott just bought a 2006 Ford Mustang and he'd like to set it up to work with his Samsung Galaxy S III. Leo says that ideally, Ford Sync would be great, but Ford doesn't allow an aftermarket install.
He'll want to get a head unit car stereo that supports A2DP Bluetooth. Leo suggests looking at the Alpine brand stereos. Having Bluetooth would allow him to play his music from his smartphone wirelessly.