Even if the timeline doesn't slip any more, I wouldn't expect 600 MHz to become available until 2020. Suppose auction applications are accepted in January 2016. If the auction itself is completed by June 2016, there's still a 39-month build-out period for the TV side of things, which means the spectrum isn't actually available for construction until September 2019. And that assumes, of course, that enough broadcasters jump in to make the auction work at all, and leaves aside the possibility of any other delays.
I do agree with Conan Kudo that the 850 MHz band should be worked on. Currently, there are two cellular licenses in that band, each having 12.5 MHz, but those licenses are not contiguous, which means some of the spectrum will probably be wasted. If the band was to be tweaked into 5 MHz block pairs once the 2G/3G sunset arrives, giving each incumbent two of the five, you could auction the fifth block pair. Similarly, the 700 MHz band uses 6 MHz block pairs when 5 MHz would be more appropriate. There is enough wasted space there that if you shifted everyone slightly, you could extract at least one more 5 MHz block pair out of the band.
- Trip