Cell phone company mergers should come with a requirement that their entire combined spectrum block go back up for open bid, with some of it set aside for new entrants.
Mergers of companies that control scarce resources have some serious tragedy of the commons problems. There should be a significant cost to doing it.
In theory, the whole point of privatizing the spectrum is to avoid the tragedy of the commons problems. This seems to have been the winning economic consensus in the 1980's and 1990's, which led to the FCC adopting the auction model for spectrum.
There is a significant cost, to the tune of $32B in this case. The spectrum they purchase is far cheaper than this - estimates for the upcoming FCC incentive auction put each winner around $15B for a 10MHz up/down slice. Besides, if you put a spectrum block back up for sale, wouldn't that help AT&T and Verizon control more spectrum since they'd be in the best position to buy the freshly freed spectrum.
Mergers of companies that control scarce resources have some serious tragedy of the commons problems. There should be a significant cost to doing it.