I installed a Bluestar unit today in my 2008 GMC Yukon Denali. I tried to document the process that I went through in case if offers any assistance to someone else in the future.
I started by very carefully removing the trim panel from around the radio:
Next I unscrewed the environmental controls and removed/disconnected the radio. This left me with quite a rats nest of wires. You can see the Onstar unit circled in red (it was labled Continental).
The J1 & J2 wires that need to go to the Bluestar unit were off the back side of the unit and were not easily accessible from the front. I decided to see if i could get to the back of the unit from a different angle. I saw there was a a little panel down by the gas pedal:
I removed the panel and was able to see the back of the Onstar unit:
The problem was I couldn't really get my hand back there to disconnect the wires. I ended up removing the metal bracket which gave me alot more room to work:
Here you can kind of see where the Onstar unit was:
Even after removing the bracket it was still a little difficult to get the J1 & J2 cables unplugged. I ended up having to use one hand going through the dash, and my other hand from behind. After a little bit of effort I was able to get them unplugged. There was plenty of slack to pull the cables down a little bit and plug them into the Bluestar unit.
After it was all setup I placed a call to my cell phone and immediately saw the notification on the DIC display:
There wasn't really anything displayed on the radio itself except the blue Onstar logo.
This ended up taking about 30 minutes to do. I like having the Bluestar unit down by the access panel by the gas pedal as it offers very easy access to the USB port.