Whatever works. This sounds like a system that would use a minimum amount of resources. Imagine a system that could transmit and receive hashes converted to Morse Code and back again at the other end. As long as the signal wasn't interrupted - like by static or overlapping band signals - we could go anywhere with Bitcoin, yet without the Internet.
There is probably a market for a handheld unit, so that you could go to a yard sale, and buy your products without the Internet being involved at all. This way there would be no NSA reception, at least not that would be useful to them.