By Greg Roumeliotis and Arno Schuetze
(Reuters) - T-Mobile US Inc <TMUS.O> is close to agreeing tentative terms on a deal to merge with peer Sprint Corp <S.N>, people familiar with the matter said, a major breakthrough in efforts to merge the third and fourth largest U.S. wireless carriers.
Japan's SoftBank Group Corp <9984.T>, which controls Sprint, will own 40 to 50 percent of the combined company, two of the sources said on Friday, while T-Mobile owner Deutsche Telekom <DTEGn.DE> will own a majority stake.
The sources asked not to be identified because negotiations are confidential.
Once terms are finalized, due diligence by the two companies will follow and a deal is expected by the end of October, though talks may still fall through, the sources said.
The deal would also face regulatory scrutiny over concerns that the U.S. wireless market is becoming too concentrated.
A successful deal would create a business with more than 130 million subscribers, just behind Verizon Communications Inc <VZ.N> and AT&T Inc <T.N>. Revenues would top $70 billion and, say analysts, there would be massive scope to cut costs.
Sprint shares jumped 5 percent in premarket trading in New York, while T-Mobile rose 1 percent.
Sprint declined to comment. T-Mobile, SoftBank and Deutsche Telekom did not immediately respond to requests for comment.
T-Mobile has a market capitalization of $52 billion, while Sprint has market capitalization of $32 billion.
SoftBank founder Masayoshi Son abandoned an earlier attempt to acquire T-Mobile for Sprint in 2014 amid opposition from anti-trust regulators concerned that consumers could lose out.
T-Mobile has outperformed Sprint under Chief Executive John Legere, who the sources said would lead the combined company.
(Reporting by Greg Roumeliotis in New York and Arno Schuetze in Frankfurt; Additional reporting by Pamela Barbaglia in London and Douglas Busvine in Frankfurt; Writing by Douglas Busvine; Editing by Bernadette Baum)