I found an interesting blog post by Boris Veldhuijzen van Zanten http://bomega.com/
and he made some good points about Fon (He also started a company similar to Fon a few years back, but later sold it). Here's a quote from a blog entry.
Having said that here is my opinion on Fon and the problems, I think, it faces;
1: It is illegal
Although Fon aims to make deals with ISPs to allow Fon on their networks right now Fon is illegal on most networks. My ISP clearly states that it isn’t allowed to share my network with other people than those that live in my house. If I open up my network to the world I’m violating the contract I have with my ISP. Wether the ISP would actually sue me is a different matter as long as Fon isn’t really successful. But you can image the ISPs opinion of Fon will drastically change if people start canceling their DSL lines because they all share one Fon router. And I’m not even talking about reselling your DSL line to other people through Fon.
2: It is dangerous
Wether or not you are allowed to share your DSL line or not either way YOU are responsible for all data that is transmitted over your connection. If your neighbor uses your DSL line to upload kiddie porn you will be held responsible. As far as the ISP is concerned YOU are uploading illegal stuff. Opening up your DSL to the world is like playing russian roulette.
3: It doesn’t work
Wi-Fi in theory is great. You switch on your Wi-Fi router and within 100 meters (according to the specifications on the box) you will be surfing the web with a 11 mb connection. In reality Wi-Fi sucks. Every electrical device in your house limits the signal of your Wi-Fi adapter. Every other Wi-Fi adapter tries to get in the same spectrum as your router and every wall limits your reach considerably. Getting your house covered is NOT easy and requires constant attention. My house in only 22 meters long but I would need 3 access points to get it covered because of all the interference from other sources. Even if every house in the world would have a Fon router installed there still wouldn’t be Wi-Fi access everywhere.
4: You won’t find it
The general idea is that you want to check your mail, open your laptop and (surprise!) there is a Fon router there. In reality 99.9% of people don’t live next to a bar, hotel lobby or restaurant or other potential place where you would open your laptop. With HubHop we went looking for individuals who lived near big squares in the larger cities. But even IF we could find someone willing to help us we often found out that they were just slightly to high in a building or far away from the square to be of any use. I think I am a prototype Fon user; always on the road and opening my laptop all the time in different places all over the world. But so far I have never accidently stumbled upon a Fon access point. My guess is I never will unless I look up an address at Fon and go search for it in some residential area.