While they overpaid (in the tech boom who didn't?), to be fair T-Mobile USA has generated billions in profits annually for a while which eases the pain a bit. Plus they're getting a decent chunk of AT&T, which should be in a really good place with T-Mobile out of the way. Mostly I think this was so they didn't have to spend the capital for a full LTE network upgrade, which would be quite an outlay.