The old adage goes that you have to spend money to make money, and that's exactly what T-Mobile's been doing. Today the fourth-place US carrier reported their Q4 2013 earnings and the results were mixed. While they added 1.65 million new customers — good for the long haul — the hyper-aggressive marketing and incentives resulted in a quarterly loss of $20 million. Granted, that's on revenue of $6.8 billion for the quarter, an increase of 39% from this time last year. But a loss is a loss.