What makes you think WiMax will reach wide penetration? Sprint is the only one investing in Wimax. I think all the other major architecture builders aren't bothering because it changes their current business model. I think it's more likely that a bubble of Wi-Fi appears across most urban areas.

Maybe Google will use the old TV frequencies to launch a new nationwide wireless IP network. It seems like a really good use of their market cap to take control of the old TV frequencies.

Also, devices will need better battery lives or a clever hack if you want to be able to listen to anywhere.fm wirelessly for 24 hours.