I wanna know where you're getting reliable GSM service for $2 a month.
I have 2 GSM phones (one with Straight Talk on AT&T, and one with T-Mobile), and I can't even get reliable connections inside my house (which is less than 5 miles from town). Much less "in the forest": at my main client's office, the T-Mobile phone doesn't work at all, and the other one only works about half the time. And only if I go outdoors and stand so I can actually see the tower (Actually, that's not quite true: about 20% of the time, I can send a text indoors with only one or two tries. And the phone rings about 10% of the time when someone tries to call me. But I can't answer it: the call drops before I can even get off a "Hello").
If you're using GSM, you'd better be designing for the Internet of Urban Things.