SoftBank and German group Deutsche Telekom, which holds 64 percent of T-Mobile, are considering a stock swap for the deal, which could be announced as early as this month, the Nikkei daily said.
The two will also discuss details of the planned merger, including ownership ratios, the business daily said.
The Japanese telecom giant is also planning to begin procedures for the approval of the US Federal Communications Commission and the US Department of Justice, the report said.
Immediate confirmation of the news report was not available.
T-Mobile ranks third among US wireless carriers by subscribers, followed by Sprint in fourth place, the Nikkei said.
Together, the pair would have 131 million subscribers, which would see them virtually match second-ranked AT&T and pose stiff competition to market leader Verizon Communications, it said.
SoftBank has long sought to combine the two firms but appeared to abandon the plan due to likely opposition from US regulators.
But the prospects for consolidation among US carriers have brightened with the pro-deregulation stance of President Donald Trump, the Nikkei said.
SoftBank chief executive Masayoshi Son was among the first businessmen to meet Trump after his election victory last year.
SoftBank’s founder pledged to invest $50 billion in business and job-creation in the United States, winning praise from Trump.
Download our app and read this and other great stories on the move. Available for Android and iOS.
