I guess it seems like a bit of a stretch at first, but they've included such a large margin for error that I think the point is still well made and their statement as a whole regarding the Hubble is probably true. SMS is probably a pretty good cash cow.
On the other hand, anyone who has experience with wireless equipment on towers knows that the costs of land/tower leases, carrier grade equipment, labor (OSHA compliance at several hundred feet in the air), maintenance, insurance, regulatory costs, cable, power, cranes, equipment enclosures (some climate controlled...yikes), spectrum licenses, and later upgrades...these costs really are HUGE even for just a few towers.
Not to mention that the connections between cell phones and cellular networks don't quite have the bandwidth capacity that high-speed ISPs and even WISPs enjoy on the pipes to their users, and the transfer of 1MB is a much bigger deal than you'd perceive if you don't take that into consideration.