Peter has a closed Wi-Fi network in his home and he decided to subscribe the Wi-Fi sharing service on the most common ISPs (including ISP A) in his area and opened his network with the necessary security rules.
From this moment on, he gets a discount from his ISP because he is sharing the network and the ISP can see that some users are using it.
John is a subscriber of ISP A so when he reaches Peter's network, he is automatically connected and is able to surf the internet within the bandwidth and time limits specified by Peter.
This way most of this country is covered with Wi-Fi networks and everyone has internet everywhere without having to pay any subscription to mobile phone networks.
ISP A wins because Peter will tell his friends how cool it is to be in ISP A when we are outside our home.
Do you think this could work? (I don't think so, but it would be a better world wouldn't it?)
edit: Hehehe this is funny. as Waldir pointed out, I've just discovered Fon's market model :P http://www.fon.com/en/info/whatsFon