Just wanted to share my success story 'converting' my defunct OnStar function in my RS 6 to Bluetooth. I considered going with the Audi BT setup (esp. when I had my RNS-E) but not having a MFSW with a convenient button to access the phone (place/answer calls) was a downside. I know I could just click the answer button on my phone, but to me the draw of having a BT setup in the car is leaving the phone in you pocket and never needing to fiddle with it.

I came across this post Convert OnStar to Bluetooth, reached out to Keith and worked out the details which involved simply pulling the OnStar 'button board' in the overhead console and shipping it to him to modify. He shipped back the board, the Costar module and everything needed to install.

Pulling the OnStar module was a PITA without a doubt. It's in the passenger footwell which is easier to access than others that are under the passenger seat but still a bit of wrestling. There are 3 nuts that hold the module in so once it's exposed it's easy to remove but the carpet is the bear of the job. There are 11 wires that need to be moved from the Audi harness over to the two Costar plugs, the instructions detail how to do that, very straightforward. There is also a GPS antenna connection that goes to the old OnStar module, so when I get another RNS-E, I'll have an easy spot to extend the GPS antenna in the shark fin.

Once the Costar unit was plugged in, turned on the ignition, went to bluetooth settings in my iPhone, synced up and everything works beautifully. Incoming calls mute the music and rings through the speakers as expected, press the white OnStar button and you answer. You can access voice dial (and of course SIRI if you have a 4S) via the white button, issue voice commands etc. The LED is fully functional and lets you know the status (synced, on a call, pairing/discoverable, etc). Voice quality is great and people I've talked to say it sounds clear. The unit has a USB port for tweaking the settings as well.

It now supports A2DP streaming for music (requires Line IN on the head unit) but a nice bonus there and something the Audi unit can't do.