T-Mobile's reinvention has been underway for a few years now, driven by the larger-than-life CEO John Legere and his Uncarrier program. While the company had succeeded in stealing customers from its rivals, namely Sprint, it seemed that strategy was also driving it to heavy losses. That changed this morning, when the company reported its second quarter earnings, and a profit of $391 million that surprised Wall Street analysts.

"We have completely reversed T-Mobile’s trajectory and started a revolution that is changing the rules in wireless," said Legere. "Now — with more than 50 million customers, 1.5 million customers added this quarter and five quarters in a row of over 1 million net new customers — we are proud to be the fastest-growing wireless company in America."

Legere is prone to boasts, but this time the numbers back it up. T-Mobile led the industry in terms of both revenue growth and subscriber growth. It still trails well behind Verizon and AT&T, which both have over 100 million wireless subscribers, but is quickly catching up with Sprint, which has around 55 million.

It's worth noting this quarter's strong financial performance was driven largely by licensing deals with Verizon, which paid T-Mobile $731 million to acquire spectrum. Subscriber growth added to revenue, but not profit. In part that may be because the Uncarrier program, which offers to pay customers early termination fees, incurs a heavy expense up front, with the hopes of holding onto those customers for the long haul.

All four major US wireless carriers had strong second quarters. Sprint also reported a small profit and said that it had trimmed its losses, with only 181,000 customers leaving over the last quarter. Verizon and AT&T both reported subscriber gains and healthy profits, par for the course among the market leaders.