FYI, I just installed a new unit on a 2009 G6 GT and it works perfectly. The vcim was in fact behind the glove box on the right side as mentioned in the other thread, but there is some kind of fan or filter enclosure in the way on my car that prevents access. Instead, I was able to reach the vcim by removing the plastic panel under the dash just behind and under the glove box. Access was easy from there. As mentioned in the other thread, the GMLAN jumper is required. I turned the mic gain down as far as possible and I'm told that the voice quality on the other end is very good.
Thanks for making such a great product; I look forward to getting a lot of use out of it!