I did not go with the Onstar phone because I am with Cingular. I did, however, get a Blue Ant wireless SuperTooth II. It is a portable handsfree bluetooth. It comes with a metal bracket for the sunvisor. The SuperTooth II has two magnets on the back and it just attaches to the sunvisor bracket. I get a call, I hit the talk button and talk. It can go anywhere, in or out of a car/truck.
As for XM - I am past my trial, had paid for one month. I called, mentioned the secret word and I am set for a full year at $77.00.

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2006 Slate Blue Metallic H3, FlowMaster exhaust, True Flow cold air intake system, Ground Force rear lowering kit, custom locking fuel door, chrome hood grill w/handle, US Speedo gauge kit (chrome and red numbers), Custom rear tire cover, chrome tail light guard, custom paint on skid plate, new pin stripping, USMC front license plate.

Semper Fi