Viral Spaces research group, based at MIT's Media Lab, has come up with an interesting Android app which aims to foster network sharing between smartphone users.
The app is named Airmobs, and works as a peer to peer Wi-Fi tethering network. The goal of the app is to increase everyone's access to Internet services, wherever they are, by sharing access between handsets. So if you're in a poor signal area or roaming and don't want to rack up obscene data charges, then you can simply leap onto someone else's network, provided someone is sharing nearby.
Of course a system entirely comprised of leeches wouldn't last very long, so Airmobs works via a system of reciprocity. Users who share access to their network will receive credits which can then be spent gaining access to other people's networks. So there's no chance of users with limited data plans taking advantage of generous users who pay more to their carriers.
The Airmobs app also contains some helpful features to prevent other users from breaching your data limits if you're sharing, and to stop them from draining your battery if your handset is low on juice. The system automatically optimises your sharing based on battery life and signal strength, preventing users from piggybacking off you when you can't really help them. You can also manually set a data limit to share, so you can be sure to save some data usage for your own needs too.
I think it's a fantastic idea, but there's of course the question of whether or not network providers will approve of users sharing network access. Sadly the app's creator, Eyal Toledano, has stated that he's reluctant to release the app on Google Play because of how carriers may react.