[EGreg]

I guess one of the biggest questions here would be authentication and reputation. You want to make sure the device is what you think it is. So they will need to have cryptographically signed messages, ie MAC, and you need to obtain a certificate as well from their server on the web in order to interact with them.

But once you have those, you WON'T need the internet in order to communicate. The vending machine could be in a basement and bluetooth would be enough.

I'm a big proponent of re-decentralizing the internet again, and the web (and physical web) is a big part of that. There's no reason why people in an african village MUST have all their cell signals travel up to a balloon and to Facebook's servers just to communicate with each other. Mesh networking and distributed power generation will bring about a revolution.