all cars from 08 up built for the US have onstar from the factory.
its a pain in the ass really, the way it is wired in, swapping out your radio can mean your airbags wont go off in a crash.
i put a non onstar ready headunit in my car, and all the airbag lights come on. And the passenger side is "off" on the indicator all the time. Even is someone is sitting in it and buckled in..
I have OnStar. It's not really a big deal. I want to keep it intact, it's not hard just a little more expensive. I wanted to get my sunroof done this wee, but I don't know if my antenna will get in the way or not.