An iPhone to iPhone to iPhone (to Mac/iPad) network...
I don't think Apple's pursuit is over. After 5 generations of iPhones, Apple has a very large installed base of devices. Include iPads and Macs and you have a blanket over large swaths of many cities. Peer to Peer is beginning to look possible.
In an upcoming iOS update, Apple could enable iOS users to opt into a plan where they would allow the ability to network with other iOS devices leapfrogging their data needs from one iPhone to the closest one, to the one further down and so on until reaching a partner's WiFi source. Apple could install very few WiFi sources, even just one in each of their stores.
Essentially, all iPhones would be interconnected peer-to-peer with each other leapfrogging data needs from iPhone to iPhone until reaching an Apple store. In large cities, there are more than enough iPhones and iPads to do this.
Apple could roll this out with iPods and iPads first since most of the installed base of these devices don't have 3G carrier connectivity anyway and then move in to iPhones as well.
Alternatively, Apple could work with WiFi @ Starbucks using this same principle. They have a great relationship with the coffee chain and in many north american cities, there's a Starbucks at every block. Surely between the distance of you and the closest Starbucks, there will be several iPhones which can be piggybacked on to reach the Starbucks signal.
The technology exists and could work on existing iOS devices. It's a matter of working out the business side of things and rolling this out fast enough to avoid angering their telecom partners before the rollout is complete and Apple doesn't need them anymore.