This has been my sideproject for the past few months. I did it by building a bluetooth client using packetdumps and decompiled Java code. I also had to make a virtual touchscreen driver. It sends the display over HDMI and everything else over bluetooth. The radio comes with a directional microphone which lets you use voice commands for a lot of the functions. Its a great setup. The sound is digital. It basicly turns your phone into your stereo.
A friend of mine has been working on this non-stop. It is a very cool end-result.