LTE is also the path for Verizon
Fragment of a discussion from Comments:AT&T to purchase T-Mobile for US$39 billion
HSPA+ is not a legitimate 4G network. Neither is LTE, it's more like 3.9G. IMO, they're just a marketing term used by ad executives to convince consumers to buy their products using a lady in a pink dress. I heard that LTE Advanced may be the real 4G, but that may be 5 - 10 years off in the future.
As for Sprint, I think they may be left out in the dark unless they choose to abandon WiMax and step up their game. With an "AT&T-Mobile" union, plus Verizon, Sprint has a tough chance in staying competitive with the top 2, unless they choose to merge with MetroPCS (another CDMA network) or be eaten up by Verizon, which I seriously doubt could happen in the near future. Just a thought.