This is the correct answer. Found this out when I was doing a ham radio antenna install on my car. The shark fin for the XM radio antenna (that I never use) sits on top of a hole in the roof, and a nice hole in the roof is a the perfect spot for a ham radio antenna, so I removed the shark fin. After disconnecting it I noticed it also disconnected OnStar, GPS, etc. It's all integrated into that fin.

Once disconnected, the car isn't going to be able to send anything even if it tried. Only question is if your car is gonna bitch at you because it's disconnected (mine doesn't).