Full price for installation is $500 in GM offerings, and you'll pay $29 every month for 1 GB of service -- exceed 1 GB and service stops -- or you can plunk down for the 5 GB service. You can use it within 150 feet of your car but there's no encryption, so a bunch of other folks can use it as well. However, if you just want to get some e-mails and directions, research a few tunes on Songza, and, most importantly, get the kids to be quiet for a spell, it just might be worth it.
[Source: Automotive News - Sub. Req.]