Using voice plan minutes over WiFi:
Thank you iFizzgig for pointing me to the Microcell!
The existence of the AT&T Microcell verifies that the necessary Gateways into AT&T's voice network already exist on the Internet, or they will soon exist when the Microcell is fully deployed.
Then, it becomes a mere matter of firmware extensions in the iPhone to mimic the single user part of the Microcell's functionality. Might even be implementable as an app?
Given the recent NYT article, I wouldn't be surprised if the capability is already in the iPhone firmware but enabled only in those markets where the cell network is badly overloaded; just guessing.
Would anyone in NYC, or SF like to do some testing?