I recently posted in a forum about how to add 3G uplink to a UAV model. This project seems really fun to me, so I'm thinking about writing the software to make it happen (a little web server and some new features for Andropilot).
However, the bummer is that some uses wouldn't be legal in the USA (given the current harsh FAA interpretation we need to operate under - <400 ft, visual range of control).
To make sure this app/feature was used 'correctly', I would have it check to see if you are in a 'long range control is legal' country. If not legal, I'd have it automatically send a mavlink RTL command if you got more than x (1?) km away from the home location.