While executives of Sprint Corp. (S) - Get Report and T-Mobile US Inc. (TMUS) - Get Report have spoken glowingly and openly about the prospects for a merger in the recent past, the two parties were uncharacteristically reserved at a Thursday investment comment.

"On Sprint, specifically, we really don't have anything new to say. " T-Mobile USA CFO Braxton Carter said at a Goldman, Sachs & Co. conference in New York. "It's almost getting to the point of fatigue."

Just a few months ago, Braxton extolled the benefits of combining with Sprint. At a June conference, he said estimates that a merger could have benefits with a net present value of $30 billion might be too low. He described Sprint's portfolio of spectrum as a "treasure trove" that would bolster a formidable wireless network.

The tune was different Thursday. "On the discussions, we've laid out the benefits," Braxston said. "We've laid out the issues on the table, and we really have nothing new to announce today on that."

Shares of T-Mobile dropped 2.6% Thursday to $61.17, while Sprint was down 1.15% at $7.76.

Sprint boss Marcelo Claure said even less. "I have been heavily, heavily advised by my attorneys to actually say absolutely no comment on M&A as you can imagine why," he told investors. "I'm really going to not comment for this time."

Back in May, Claure said at a May conference that a combination of the two would create a "turbocharged maverick" that could shake up the U.S. wireless business.

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Claure hinted in an August media call that a mega-deal involve Sprint would come together "in the near future." He acknowledged that a deal with T-Mobile would have the highest payoff but would face regulatory risk, in a call with the media after the earnings presentation. Claure also noted that Sprint backer and Chairman Masayoshi Son had interest in cable operator Charter Communications Inc. (CHTR) - Get Report .

For his part, in August, Son told investors of Softbank Corp., which owns 85% of Sprint, that a major deal involving the U.S. wireless carrier was likely to come soon.

While merging the third- and fourth-largest wireless carriers makes business sense, it may present difficult choices for ownership. Son backed Sprint with the ambition to build a wireless power in the U.S. through acquisitions. T-Mobile backer Deutsche Telekom AG was willing to sell years ago, but has no real pressure to exit the investment as long as its U.S. wireless venture takes market share from its rivals and grows its business.

Even if the owners reach an agreement, there is no guarantee that regulators would approve a deal that would remove one of four wireless national carriers from the market.

The change in tone could reflect that talks are at a difficult juncture but still could produce a deal.

Claure observed Thursday that things could look much different at next year's Goldman conference. "We might be part of a bigger wireless carrier or who knows we might be offering some broadband or something different," he said, "so I guess the next year is going to be a different year when we sit here." Sprint could also still be independent.

T-Mobile's Carter suggested that running a company for a strategic outcome rather than building value through operations is no way to do business. "The whole management team should be replaced immediately because that's not the true path to value creation," he said.

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Editors' pick: Originally published Sept. 14.