"This is a transformative transaction for Sprint that creates immediate value for our stockholders, while providing an opportunity to participate in the future growth of a stronger, better capitalized Sprint going forward," Hesse said.
Son, a graduate of the University of California, Berkeley, said he was only 16 when he ventured alone to the U.S.
"I am happy to be able to tell you today of my big comeback to the U.S.," he said. "This is going to be an even bigger challenge."
Before Monday's deal, the biggest overseas acquisition by a Japanese company was Japan Tobacco Inc.'s purchase of Gallaher Group of Great Britain in 2007 for about $19 billion.
But the strength of the yen, with the dollar plunging to 78 yen from about 85 yen two years ago, is encouraging Japanese companies to go shopping.
Son, an unusually risk-taking and innovative executive in a corporate culture that tends to favor a staid conservative approach, acknowledged the big question is whether his overseas foray will succeed.
"I am confident," he said.
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