Welcome to Elcova Forums and congrats on your new awesome truck.
The call/answer button that you see on the steering wheel is for the Onstar only. 08 H2 doesn't have bluetooth only the 09 model.
I replaced my original radio with oem nav radio (p/n 25846421) came directly from an 08 H2. I also installed gps antenna (p/n 25918632). I have to run a VSS wire and voice wires from the Bose amplifier so i can hear the turn by turn navigation and also for the voice command. I turned off the rearview mirror pop-up camera 'coz i prefer to use the bigger screen on the nav radio. I also can watch videos from the driver seat while in park.
If i have to do it again i will go with the harddisk oem navigation
http://www.ebay.com/itm/2007-2013-CH...15a83b&vxp=mtr
I don't need a bluetooth with my set-up as i have a subscriptions with OnStar with cellular line (my H2 has it's own phone number).
If you want bluetooth with oem navigation, you have to replace the VCIM module with bluetooth from an 09 H2, '11 Cadillac CTS or Chevy/GMC trucks.
Hope this helps!
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2008 Hummer H2 Luxury Edition
Toyo MT 38x13.50x18 on Rockstar. Green keys. 2" rear spacers. 1" bodylift. Cognito UCA, steering bracket, front stab links. Bilstein 5100 shocks & steering stab. Moog inner/outer TR, pitman, idler arm & bracket with remote zerk. E&G Classics fender flares. ARP 434-1301 ex. man. stud kit. Airaid perf. air filter. Crown brake lines. Warn PowerPlant HD. Rubberduck UCP. Gobi Ranger roof rack. DDM Tuning 55W HID Hi/Lo headlights. Hella fogs. Evans waterless coolant.