To elaborate, Sprint and T-Mobile have been trying to merge, arguing that scale is fundamental in competing in the market. Regulators have argued that 4 carriers are essential to keeping parity and competition in the market.
Actually Sprint and T-Mobile have never officially tried to merge. So far all the executives have done is deny that such talks are in progress.
At one point AT&T tried to buy T-Mobile, citing Verizon being bigger as why it was okay. They even put a bunch of money on the line if it fell through. Regulators decided that either they wanted 4 parties, or that Verizon would be forced to buy Sprint to compete, leaving 2 parties. (I am not 100% certain which they said was the reason)
Actually, Sprint and T-Mobile are both on-record as planning on merging. They aren't planning to do so in the immediate future, but they both see the long-term end game being just three carriers in the entire US.
All they are waiting for is the DOJ to make a mistake and let it slip through.
