The sources asked not to be identified because the negotiations are confidential. Sprint and Deutsche Telekom declined to comment. T-Mobile and SoftBank did not immediately respond to requests for comment.
SoftBank's Son abandoned an earlier attempt to acquire T-Mobile for Sprint in 2014. Under that deal, SoftBank would have been in control of the merged company, with Deutsche Telekom becoming a minority shareholder.
Since then, T-Mobile has outperformed Sprint under Chief Executive John Legere, who the sources said would lead the combined company.
Son In Trump Tower
Earlier this month, Federal Communications Commission Chairman Ajit Pai gave a potential boost to a tie-up when he recommended that the FCC find for the first since 2009 that there is “effective competition in the marketplace for mobile wireless services.”
The FCC is set to vote on Tuesday on the proposed annual report on the state of the wireless competition market required by U.S. Congress.
T-Mobile and Sprint will likely tout planned investments in 5G and their network that would create jobs, though combining operations would also lead to layoffs, said Roger Entner, an analyst at Recon Analytics.
"They will argue that the track record of T-Mobile and Sprint shows they are vigorous competitors and that this will not cease to be the case after the deal," said Entner.
Son made headlines in early December when he appeared in the marble lobby of Trump Tower in New York alongside the president-elect, dressed in a red vest and red tie nearly identical to that of the tycoon turned commander in chief.
He was among the first in a series of Asian billionaires and leaders to pay a congratulatory visit to Trump, who won office in November on a platform that focused on national security and protecting U.S. jobs.