Looks like I'll be making two version of this product.
The "BlueSTAR" unit, which interface to the motorola HF850 hands free car kit and uses the OnStar mirror buttons and microphone, and passes the audio into the cars amplifier, and...
The "HyperSTAR" (named after HyperBoimmv) which simply mutes the radio over class 2 and is triggered with an external mute input. You can use any bluetooth kit with this version, but it will not interface to the onstar mic, buttons or pass audio to the radio.
The HyperSTAR unit should work in all GM class 2 controlled vehicles without Onstar.
I'll detail all of this again in more detail on my website once I get it up and running.
www.costartech.com