Japan's Softbank Corp. said Monday, Oct 15 it will buy a 70% stake in U.S. mobile carrier Sprint Nextel Corp. for about $20 billion in the biggest-ever overseas acquisition by a Japanese firm, MarketWatch reports.

The deal is designed to carve a potentially lucrative opening in the U.S. for Softbank, Japan's third-largest mobile carrier. At the same time, it will provide the third-largest U.S. wireless operator an immediate infusion of cash, helping it compete better with bigger rivals in one of the world's biggest and most lucrative markets for smartphones.

In a statement, Softbank, which also has a range of Internet operations, said it would acquire a majority stake in the U.S. carrier by buying $8 billion of shares directly from Sprint and then buying another $12.1 billion of shares in the market.

The deal would transform Softbank, a comparative newcomer in the telecommunications industry, into one of the world's largest telecoms groups with about 90 million subscribers once combined with Sprint.