I'm looking into ordering one off Ebay and confirmed that it does require a valid GSM subscription to a wireless carrier. Here in Canada the cheapest is FIDO with their $15/mo plan that offers unlimited texting. If you wanted to call it to listen to the microphone for some reason that would cost you an addition .20c / min. So basically a $15/mo insurance plan. I'm impressed with the research and applications that I've read in the posts above. Seems like a really smart idea if your Phantom goes down in a field of tall grass/forested area, etc.
I've also watched a number of youtube vids of crashes. It seems that the gimbals rarely survive well but for the most part the Phantom shell seems to weather most incidents. Replace a gimbal maybe a prop or two and you're back in the air. Not bad at all! Even better, don't crash lol