You're dreaming if you really think that WiFi (or WiMax) will present the sort of coverage and availability that is already in use on 3G networks around the globe, have you any idea how many routers you'd need? http://feetup.org/blog/tech/How-many-routers.html

Just one further thought to kill the WiFi hype, how are you going to handover a connection from one WiFi hotspot to the next?