Make them share
I would not be adverse to letting V or AT&T own as much as they can afford to buy as long as they are required to easily share it with competitors at a reasonable cost.
Not sure of the mechanics of this concept, will let the lawyers and technical experts work that out.
The difference between genius and stupidity is that genius has its limits.
T-mobile is already testing spectrum sharing with government owned bands, AT&T and Verizon hate the idea obviously because it decreases their capability to starve all of their competitors by buying spectrum and sitting on it.
It would be a wonderful thing for wireless competition, but with our current government and regulatory agencies, not to mention the fact that Verizon and AT&T seems to have bought the fcc, it will have a tough time.