Rui CarmoI was going to harp on about Fon's utterly pointless approach to providing what is sure to be an extremely patchy service by being a parasite atop other networks and breaking their TOS, but Techdirt beat me to it.
Previously: Debunking Punditry and A Dose of Perspective, wherein I explain why Wi-Fi (meshed or otherwise) won't fly for this sort of thing. There are plenty of other examples scattered throughout the site.
And yeah, I'm biased. But like Jim Hughes put it, HSDPA is "... a little simpler than relying on 888,219 routers to be all working".
Still, the dual SSID feature Om Malik mentions is intriguing, and something I could have used back when we were designing our own Wi-Fi hotspot offering.