Basically with a bit of work you should be able to implement something approximating a tty type interface over this, which means that you could (theoretically) sit in the car park running a metasploit session on an evil box hooked into the target network in a very difficult to detect manner.

It also provides all kinds of interesting potential capabilities for anonymous communication across crowded networks. This could be great for co-ordinating drug deals or suchlike but is probably better still for co-ordinating protests and exporting information when GSM's down.