What: Shares of No. 4 wireless carrier Sprint (NYSE:S) skyrocketed Tuesday morning, up by 19% as of 11:52 a.m. ET, after the company reported better-than-expected earnings.

So what: Net operating revenue came in at $8.1 billion, which all translated into a net loss of $0.21 per share by the time you reach the bottom line. While the top line was a little light compared to the $8.25 billion consensus estimate, Sprint lost less than the market was expecting. But more significantly, there are signs of progress with the turnaround.

Now what: Perhaps the most important figure was that Sprint added 366,000 postpaid phone customers, the highest level in three years and a major improvement from the 205,000 net postpaid phone customer losses it put up a year ago. CEO Marcelo Claure said that costs are coming down "faster than expected," as evidenced by the better-than-expected net loss. Sprint also raised its full-year guidance. Fiscal 2015 adjusted EBITDA was previously expected in the range of $6.8 billion to $7.1 billion, and Sprint is boosting that forecast to $7.7 billion to $8 billion.