Notwithstanding the security issues it sounds like it could be a non starter as the majority of ISP's are none to happy with the idea. FON are trying to convince them that although some people will undoubtedly hop on the free internet access bandwagon at the ISP's expense that the customers they actually have signed up to broadband will be more loyal. Since it is unproven as to the effects on bottom line it will be interesting to see if any ISP's actually buy into that rationale.
The other issue facing FON is that there are projects in many cities around the world to provide free hotspots anyway. Be interesting to see how it all pans out.