Could MetroPCS take over T-Mobile's slot in the Tier I carrier ranks?

If AT&T succeeds in its bid to buy T-Mobile USA -- and it looks like it will -- the Tier I carrier ranks will shrink to just three operators. In today’s highly saturated mobile market, it’s hard to envision a new nationwide operator emerging, given the scarcity of spectrum and the difficulty of raising a voice and data network from the ground up. But MetroPCS seems to have just such intentions.