We already have this. It's called white space technology and has so far amounted to pretty much nothing. The technology is immature and expensive plus it provides very little bandwidth.
Cool, thanks for the heads up. After wiki-ing around, it looks like current whitespace technology is hobbled by forcing the broadcast device to get permission from an FCC database in order to transmit. With that constraint, I am not surprised it hasn't taken off.
What segments of the spectrum allow this technology for public use? How do those compare to what ATT/VZN own?