NEW YORK ( TheStreet) -- Softbank reached a deal Monday to acquire a 70% stake in Sprint Nextel ( S - Get Report) for $20.1 billion.

The merger was approved by the boards of both companies. It still needs approval from Sprint shareholders and U.S. regulators. The deal, Softbank said, is expected to be completed by the middle of 2013.

Sprint is the No. 3 wireless provider, behind AT&T ( T) and Verizon Wireless. The deal will give Sprint more capital to use to compete against its much bigger rivals.

Softbank's acquisition of Sprint is the largest ever foreign acquisition by a Japanese company. Softbank is Japan's third-largest mobile carrier.

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Sprint confirmed last Thursday that it was in discussions with Japan's Softbank about a possible "substantial" investment.

Softbank said it would buy $8 billion of shares directly from Sprint and then another $12.1 billion of shares in the open market.

Sprint Nextel shares closed Friday down 3 cents at $5.73.

-- Written by Joseph Woelfel

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