I think perhaps for home broadband (read wifi) use sure, we could free up another 200 mhz easy - as replacement for mobile broadband.. you wanna look between 600-1900 mhz there, anything much above 2.5 is too high (read expensive) to build a mobile network with because of site spacing.

Much of what's in that band is allocated for point to point microwave and satellite, I'd also caution you, one mans 'wasted spectrum' is another 'vital important service' both of which can be technically correct at the same time.