There's a new Wi-Fi sharing service launching at Demo 07: Whisher. This service competes with Fon, but has a very different architecture. (See News.com story.)
Fon asks its customers to install Fon-powered Wi-Fi access points on their broadband connections, and it makes them all into a global shared network. Whisher, by contrast, collects the access keys to the existing routers that its subscribers already use. In other words, to put your broadband connection on the Whisher network, you give the service your Wi-Fi access point's ID and security code (WEP or WPA key), and then Whisher holds that information in proxy for its other subscribers.
Subscribers use the Whisher software to connect to access points on the Whisher network. The actual passwords that Whisher transmits are not revealed to subscribers.
Clearly, it's a much simpler way to build a co-op network of access points, since it doesn't require dedicated hardware.
It is, however, a scary proposition from a security perspective. With Whisher, anyone who gains access to a Wi-Fi access point can put it on the network. Whisher founder Ferran Moreno said, "As long as you can connect, we assume you are the owner." But that's not the case: Once you give your network's Wi-Fi key to friends or employees, any of them could put your Wi-Fi on the Whisher network, and you might never know it--until you find strangers on your LAN and no bandwidth left for the people who own it.