Individual WWAN access through WLAN?

How about if each person with a wireless internet connection can dowload software that will allow them to allow anyone within range to use their wireless network for a small fee. If enough people in large metropolitan areas were to do this could you create enough of a newtork at much lower cost, basically allowing people to connect to the internet on a pay-per-use basis as they are mobile. Extending the thought, could you build a new class of cellular phones that work across this constellation of individual WLANs if they exist, only utilizing the cellular bandwidth if no such connection exists. What would that do to the cost of cellular calls? Could you build a partnership with the telecoms/cable providers so that they get a kick back in such arrangements. Would they then not try to build out such networks on their own?