there have been several stabs at similar problems using unlicensed spectrum; you pay people to use wimax or wifi wireless routers running software you provide. Your software allows your other customers to connect to the internet through those routers. From there it's easy enough to provide voip phone service. If you control the software on the routers, it's easy enough to set up authentication so only third parties that pay you can connect, and to rate-limit those third parties to something reasonable.
But it's a difficult thing to carry off. Several companies, I believe, have tried and all have failed. (I can't remember the names of any of those companies right now; I don't know if that's 'cause I'm tired, or if that's 'cause I'm actually remembering a conversation about a business that someone wanted to start that never happened, or if I'm just making this up wholecloth. None the less, it seems like a direction from which you could attack the market using unlicensed spectrum. You would have many obstacles, but it seems possible, at least in high-density urban areas.)
Cringely proposed that Wal-Mart install wimax routers in every store and thereby essentially blanket the country in coverage. I don't know enough about wimax or wimax phones like the HTC Evo to know if you could provision any wimax router to make voice calls, but I do like the thought that someone in an entirely different business could disrupt the ridiculous monopolistic profit machine that is today's cellular market.
