FORTUNE — Could Japan’s SoftBank and China’s Alibaba be the one-two punch that knocks leading U.S. mobile and e-commerce companies off their game?

When the online retail juggernaut Alibaba lists in New York — perhaps as early as next month in what is expected to be the largest market debut ever by a technology company, surpassing Facebook’s $16-billion I.P.O. — SoftBank will have 34 percent stake.

Much has been made about the 40 percent ownership stake that Yahoo YHOO must sell when Alibaba goes public, and for good reason: The Sunnyvale, Calif.-based company’s financial performance has long been pinned to its piece of the fast-growing Chinese company, which could be worth an estimated $10 billion. Without it, the company must find its own growth.

But SoftBank has no plans to cash in its stake. That is perhaps a little surprising, given that the company’s billionaire chief executive, Masayoshi Son, has piled on about $90 billion in debt resulting from a very aggressive acquisition spree. The cheerful and diminutive Son, described by some as Asia’s Warren Buffet, is considered to be a crafty businessman with a very ambitious vision for the future of the global Internet and his company’s place in it.

“What makes us fundamentally different from other companies is that our background is in the Internet, not simply telecom operations,” Son wrote in SoftBank’s annual report. “The SoftBank Group’s goal is to become the global No. 1 in mobile Internet. Our vision for the Group is to enable people around the world to lead enriched lifestyles by enjoying a diverse spectrum of services and content, such as music, video, e-commerce, and financial settlements.”

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Son has watched the value of his company’s shares double in the past 12 months, resulting in market capitalization of $98 billion. In 2013, he made a $21.6 billion acquisition of Sprint, the third-largest U.S. wireless carrier. Emboldened, he has now expressed interest in acquiring T-Mobile, the fourth-largest U.S. carrier, and is expected to make a formal bid this summer.

U.S. regulators have been wary of combining the No. 3 and No. 4 U.S. carriers, but Son has promised the mother of all price wars with Verizon VZ and AT&T T if they allow him to move forward with his plan.

Alibaba — which sold merchandise valued at more than $248 billion last year, more than Amazon AMZN and eBay EBAY combined — has suggested that its decision to list in New York rather than Hong Kong or Shanghai was informed by its plan to grab market share from America’s e-commerce leaders.

“SoftBank, with its acquisition of Sprint, is a serious threat to local operators because it can build on a local, established company,” says Karsten Weide, an analyst at the market research firm IDC. “For Alibaba, it will be much harder to pose a challenge to Amazon and eBay, because they have no local presence to speak of yet. Also, they will face similar cultural hurdles entering the U.S. market as American companies have encountered launching in the Chinese market.”

Like eBay, Alibaba relies heavily on third-party retailers to drive business over its platform, giving it less control over what is bought and sold. (Amazon sells many of its good directly.)

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SoftBank’s Son doesn’t see any of this as a hurdle. He believes he can leverage his stake in Alibaba, a company he describes as an “indispensable strategic partner,” to create synergies between the two companies as they increase activity in the U.S. At the heart of Son’s global expansion plan is the creation of an Internet and mobile ecosystem that uses telecom infrastructure as a platform for delivering an array of services beyond voice and data. “Controlling the infrastructure means controlling the world of the Internet,” Son wrote in the annual report. “This is the rationale for our involvement in the telecommunications businesses.”

Not everyone is bullish on Son’s grand plan. “Sprint needs to give U.S. customers a mobile product that’s far more compelling than what AT&T, Verizon and T-Mobile offer in order to win customers back,” says Bill Menezes, an analyst at the market research firm Gartner. “Giving them another way to buy things when they already have Amazon, e-Bay, Google and other entrenched options is not going to change that.”

IDC’s Weide agrees. “Even if Alibaba launched in the U.S. today, it would be at least three or four years before it would present a serious challenge.”

Time will tell. But as a man who holds a stake in more than 1,300 companies, Son seems prepared to wait.