Installed in my 2004 H2:
Sidebar: I lost my flash in the middle of the install so some of the Pictures may be lite on quality
Keep engine off
Put Emergency Brake on
BlueStar unit:

Remove Console and Armrest:

Turn key to accessory, don't start engine.
Shift to 1st gear.
Using a T10 Torx losen set screw on front of shifter. Shift to neutral and remove by lifting straight up:

Remove cup holder and Shifter assembly by pushing straigt up from underneath.
Side note: This is a good time to clean up the Cup Holder and assembly. You can borrow Wifey's toothbrush if she pissed you off!

Take a look down inside near the shifter. You may find s bunch of coins. I removed them so they wouldn't jam up anything. Bonus of $1.07

Remove bolt to the right of Shifter assembly as well as 2 hex screws from front of console:

Lift and slide back console so you can reomve the center bezel.
Remove Center bezel by removing 2 hex bolts on the center bezel and pulling bezel straight out, unclipping 3 push clips. Once removed unbolt the Onstar unit:

Unplug 2 white plugs form back of OnStar.
(Make sure you don't remove the white antenna plug) 2 plugs are connected together by grey foam. Carefully cut the foam in order to seperate the 2 plugs. Re-route the 2 white plugs up and to the right near the glove compartment. I put the BlusStar unit in the cavity behind the radio.
Make sure to keep BlueStar circuit board away from any metal where it could possibly short out.

I woulg guess 2 hours from start to finish. Mine took longer but I messed around with some other wiring while I had eerything removed.
Good Luck and let me know how it goes!
Hope this helps!
