By all accounts, Sprint Corp (NYSE:S) should have responded bullishly to its fiscal third-quarter numbers unveiled on Tuesday morning of this week. The wireless carrier added more postpaid subscribers than rivals Verizon Communications Inc. (NYSE:VZ) or AT&T Inc. (NYSE:T), and the loss was whittled down to almost half of what it was in the same quarter a year earlier. Revenue is decidedly growing again.

And yet, there it is. Sprint stock popped briefly early in Tuesday’s trade, but by the end of the day had given most of the gain back. It lost more than its fair share of ground on Wednesday too.

Thursday’s not so hot either, leaving more than a few S stock owners wondering “What’s it going to take to get — and keep — this stock moving?”

The answer really isn’t as elusive as you might think, though a word of caution … the die-hard believers in Sprint stock’s turnaround story might find the answer more than a tad frustrating.

Cash Flow Tells the Story for Sprint Stock

For the quarter ending in December, Sprint lost 12 cents per share on revenue of $8.5 billion. The top line was better than estimates of $8.29 billion, and the loss was a significant improvement from the loss of 21 cents per share of S stock booked in the same quarter a year earlier.

What’s wrong with that? Nothing, on the surface. Indeed, it would be naive to think a great deal of the post-earnings weakness isn’t anything other than profit-taking. Sprint stock is still roughly 200% higher than where it was trading at this time a year earlier, and it’s prudent to play defense in this situation.

In the bigger-picture though, the institutional investors who really need to get behind the company’s efforts to prod Sprint stock upward for the long haul just can’t get past a couple of big, even if obscured, stumbling blocks. One of them is cost-containment.

As promised (in earnest) by CEO Marcelo Claure in late-2015, the company is cutting costs (relatively) in an effort to move to a state of profitability. What the company is saving in operational costs, however, is largely being offset by investments … investments in leased devices, to be specific. They aren’t operational costs, but they’re real costs all the same. For perspective, capital expenditures on leased devices rolled in at $767 million last quarter, versus only $358 million for the same quarter a year earlier.

There’s a primary suspect in the matter — the leaseback deal with Mobile Leasing Solutions LLC announced in 2015 is increasingly looking like what it is rather than what it was supposed to be. It was billed as a means of cost cuts. In reality, it’s merely a reconfiguration of the company’s total expenses. The end result is a persistently negative free cash flow. FCF was a negative $646 million last quarter.

S Stock: Debt Has Become Debilitating

The other impasse Claure is going to have to address sooner than later is its debt, or more specifically, the interest expense it incurs due to that debt.

Some have called Sprint stock’s debt a ticking time bomb. They may have been right.

To its credit, the company essentially refinanced a portion of it $37.3 billion in total debt last quarter, issuing $3.5 billion worth of notes using spectrum as collateral and retiring $2.3 billion worth of its more expensive debt obligations. Moody’s even upped Sprint’s credit rating last month.

It’s still not enough, however. Last quarter’s interest expense was still a whopping $630 million, well up from the $542 million in interest payments it made in the same quarter a year earlier.

Worse, a closer look at the balance sheet reveals that of its $30.7 billion in long-term debt, $6.5 billion of it is now also listed as a short-term (a year or less) obligation.

That’s more than twice the figure it was a year ago, and 2017 should be a relatively light year in terms of the amount of debt coming due. Come 2018 and 2019, its maturing debt will pop back to 2016’s challenging levels of more than $3 billion.

It leaves the company in something of a cash crunch situation no matter how good its new financing terms are.

Bottom Line for Sprint Stock

To be fair, Claure is making fiscal progress; S stock isn’t quite in the dire straits many thought it was in a year ago. It still not enough of an improvement, however.

As much as Sprint has managed to cull some expenses and garner more than its fair share of new subscribers, at the end of the day, it has helped very little … in a fiscal sense. The situation for S stock is apt to get worse before it gets better too, as its financial obligations continue to swell at the same time it’s likely committing to even more investment in its 2.5 Ghz LTE network.

Sprint stock can only defy the laws of math for so long.

As of this writing, James Brumley did not hold a position in any of the aforementioned securities.