So, I've had ambitions before about carrying around an open mobile router that anyone around me could use. I just found out about a company trying to do that.
It's a simple mobile wifi, that you leave open (without being password protected) and every time someone else starts using your connection (which albiet will slow you down a little), you each get 100Mb free of extra data to use. After they use the 100MB, they can start paying per GB at the rate as everyone else.
The website is "yourkarma.com"
The wireless signal uses the WiMax towers, I think, so it's nonexistant connection outside of major cities for now.
I'd try it out if I didn't just move to Sweden...