Regulatory hurdles and disputes over control of a combined organization stopped previous discussions on mergers. The current negotiations between Sprint and T-Mobile are not complete, said the people informed on the matter, who spoke on condition of anonymity because the deal was confidential. The moment could change, or the conversations could fall apart, they warned.
A merger would fulfill a long-frustrated dream of Sprint's majority owner, SoftBank of Japan. When SoftBank took control of the US company in 2013, its ambitious leader, Masayoshi Son, boasted of defeating Verizon and AT & T in its own backyard. But to do so, he needed a larger platform than Sprint alone and quickly began conversations to buy T-Mobile, which, at $ 55 billion, has more than double the market value of Sprint.
But in two rounds of talks, in 2014 and last fall, Mr. Son was unable to complete a deal with the controlling shareholder of T-Mobile, Deutsche Telekom de Germany.
What is at stake is great for both sides, but especially for Mr. Son. Sprint has lost billions of dollars and millions of subscribers, while getting into debt, since SoftBank took over. In contrast, T-Mobile, powered by an enormously popular unlimited data plan and an aggressive marketing campaign, jumped on its embattled rival to take third place in America's wireless ranking.
Mr. Son and SoftBank have weighed several possible, if not plausible, combinations for telecommunications, including flirting with an agreement with Charter. But the objective has always been to bring together the third and fourth largest operators in the country.
"This agreement is probably more necessary for Sprint than for T-Mobile," said Amy Yong, research analyst at Macquarie Capital.  This time, Mr. Son and Deutsche Telekom appear to be closer to closing an agreement on the control of a combined carrier, said the people informed on the matter. Deutsche Telekom would own approximately 42 percent of the new company, but would retain the majority of its shares with voting rights, the people said.
Executives from Sprint and T-Mobile declined to comment.
Even if an agreement is reached, both sides would face regulatory scrutiny.
A merger would have to be reviewed by the Federal Communications Commission, which would determine whether the agreement would create too much concentration within the wireless industry and whether it would be in the best interest of the public.
Offers of this size also receive regulatory reviews by competition defense officials at the Department of Justice or the Federal Trade Commission.
Tom Wheeler, president of the FCC in 2014, announced that he would not allow the number of national wireless operators to be reduced to three out of four. The Justice Department made similar comments at the time, saying that consumers would be harmed without four options for mobile service providers.
But the regulatory image has become brighter under the Trump administration. SoftBank executives met last year with senior management to evaluate possible Sprint deals, while Mr. Son has courted President Trump with the promise of $ 50 billion in investments in US companies.
FCC President Ajit Pai criticized the strict approach of the pre-competition management in the wireless industry.
"I do not think any regulator that embraces regulatory humility and intellectual honesty about economics can say if three, four or five is the optimal number," said Mr. Pai. he said in a 2017 interview with Recode, referring to the number of operators operating with any scale in the United States.
The Department of Justice, whose antitrust division is headed by Makan Delrahim, has been difficult to predict, analysts say. Mr. Delrahim is suing to block the purchase of Time Warner by AT & T, saying that the agreement would damage the competition and lead to higher prices for the consumer.
Officials of the F.C.C. and the Justice Department declined to comment.
Consumer groups may protest the deal. Sprint and T-Mobile are seen as important alternatives to larger operators, and have offered unlimited data plans, while others have limited them. Sprint and T-Mobile were also the first operators to allow people to unlock their phones.
These have been widely seen as pro-consumer movements, and T-Mobile in particular has shown little need to merge with Sprint, said Gigi Sohn, former senior adviser to the FCC
"T-Mobile's pricing and marketing actions have driven AT & T and Verizon to change their own prices, data plans and marketing for the benefit of consumers," he said.
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