Paul Milgrom's auction design keeps everyone guessing. Anyone who tells you she is sure of the outcome doesn't know very much. I was so wrong the last time I'm not even trying this time. Wall Streeters I respect, including Craig Moffett and John Hodulik, believe the phone companies + Comcast will find it very hard to bid more than $30B-$40B.
That will let them split about 70 MHz except in a few big cities if no one plays the spoiler. AT&T 4G customers run in 20 MHz. That would be a good outcome for the carriers. The last auction had prices about three times as high, presumably because Charlie Ergen made an attempt to corner the market.
AT&T has 40 MHz of completely empty spectrum ready to put to work, enough to create a Verizon-sized network. Verizon CFO Fran Shammo said Verizon bid so high last time they could have built the same capacity for a third of what they spent.