Rumors of a merger between T-Mobile and Sprint, the nation's third- and fourth-largest wireless carriers respectively, have been swirling all year. As the summer wears on, though, analysts say Sprint's prospects for buying out T-Mobile are looking increasingly grim — and that meanwhile, T-Mobile has everything to gain if it simply holds out for a better deal.

The latest in that saga came on Friday, when the Federal Communications Commission said it was circulating a proposal to prevent cellular companies from jointly bidding on the wireless airwaves that carry consumers' cell phone calls and mobile data, at least in the biggest spectrum auction of the decade. T-Mobile and Sprint have reportedly been planning to spend $10 billion together to buy up access to those airwaves in that auction so they can grow their networks. While an FCC blog post didn't explicitly mention either T-Mobile or Sprint by name, it was clear who the targets of the proposal were.

"Our goal is to promote the participation of as many parties as possible in the auction," wrote Roger Sherman, the head of the FCC's wireless bureau. "If two of the largest companies are able to bid as one combined entity in the auction, their combined resources may have the effect of suppressing meaningful competition."

Telecom analysts are taking this as yet another sign that the FCC is very skeptical of letting Sprint and T-Mobile get too cozy. That argument was further bolstered when a French company, Iliad, said last week it planned to make a bid for T-Mobile, too. With the pressure now growing on Sprint to seal a deal before it gets snatched away, the picture for T-Mobile is looking better and better.

T-Mobile and Sprint have reportedly been in talks for months on a potential merger, though nothing official's been announced. Sprint argues that a deal would allow the combined company to better compete against AT&T and Verizon. Perhaps T-Mobile agrees on some level, but so long as it remains independent, it'll be defining its own interests and prioritizing them over Sprint's.

In fact, it's not clear why T-Mobile would even want to commit to a merger now, according to telecom analyst Craig Moffett. Forestalling a merger with Sprint would give T-Mobile more of a chance to let its aggressive new business strategy play out. Agreeing to a merger now might mean cutting it off early.

"T-Mobile’s value is rising while Sprint’s is falling," Moffett wrote in a recent research note. "Indeed, at current run rates, T-Mobile will pass Sprint in the number of post-paid phone subscribers in less than a year."

Moffett added that even if T-Mobile's "Uncarrier" momentum eventually peters out, it still comes out ahead if it can simply "outrun Sprint" indefinitely.

Waiting beyond the 2016 elections could benefit T-Mobile too, if the race produces an administration more amenable to a Sprint-T-Mobile merger, according to telecom analyst Paul Gallant, "particularly if one or both companies falter."

Between then and now, the spectrum auction could change the fortunes of both firms. Without enough money, going up against the likes of AT&T and Verizon will be difficult. The FCC has explored putting restrictions on how much spectrum the top two carriers can buy during the auction, which is scheduled for 2015. Sprint and T-Mobile evidently think that may not be enough, considering their interest in bidding together on spectrum. But in an e-mail, Moffett said that T-Mobile's long-term future looks sunny enough without all the jockeying over spectrum.

"At this point, anything that reduces the chance of a shotgun wedding to Sprint is good news for T-Mobile," he said.