^^^ Not true on my Envoy. I have both XM Satellite and Onstar and I have 2 anttenas. The Onstar anttena is the one that sticks up 2 or 3 inches on the roof. the XM is a 2x2x2 block/square on the roof.
I also do not want an anttena on the roof but do want satellite radio and HD radio. Houston has crap for rock stations and the xm comedy is FUNNY!!!