Softbank may be eyeing more than just a stake in Sprint, say analysts who view Clearwire as a potential factor in the companies’ buyout talks.

Sprint confirmed yesterday that it is holding discussions with Softbank for a “substantial investment” from the Japanese operator. The size of the investment remains unknown, but Sprint said the stake could be large enough to “involve a change of control.”

Analysts following the announcement now speculate that Softbank may be looking to acquire a portion of Clearwire as part of the deal.

BTIG Research Analyst Walter Piecyk points out that Softbank and Clearwire are both building TD-LTE networks in the 2.5 GHz and 2.6 GHz bands and are both members of the Global TD-LTE Initiative, whose other members include China Mobile.

“Yet investors have remained skeptical about both TD-LTE and the 2.5/2.6 GHz spectrum,” Piecyk said in blog post, referring to comments from former Verizon Wireless CEO Dennis Strigl during a CNBC interview dismissing the possibility of Softbank including Clearwire in the Sprint deal. “That skeptical view is shared by many and, ironically, or perhaps appropriately, could have been one of the deal motivators for Softbank, which like Clearwire is investing in its own 2.5/2.6 GHz TD-LTE network in Japan.”

By investing in both companies, Softbank would be able to use Sprint’s existing infrastructure to deploy service using Clearwire’s spectrum. Building a new network “could cost nearly double. Sprint also brings 48 million customers, a brand and distribution to the table. The industry is too mature for a new entrant building from the ground up,” Piecyk said.

Macquarie analysts Kevin Smithen and Zach Horat said Softbank may purchase the portion of Clearwire not owned by Sprint, the WiMAX operator’s largest shareholder.

“A large issuance of Sprint shares to Softbank, followed by a buyout of CLWR’s remaining equity (the portion Sprint does not own) and a dividend recapitalization, is the most likely scenario, in our view, if the press reports are accurate,” the analysts said in a research note. “This would serve to provide Softbank with ownership control and consolidate CLWR and S.”

The analysts were skeptical that Softbank would look to purchase a controlling stake in Sprint, calling it “unattractive and unlikely.”

Keeping in mind that Huawei is a major TD-LTE supplier to Softbank, a minority investment also removes any potential foreign ownership concerns related to Sprint’s federal government and local public safety subscribers, they said, referring to a recent government report that categorized Huawei as a security threat because of its alleged ties to the Chinese government.

Smithen and Horat estimate Softbank’s investment in Sprint will be much smaller than the $12.8 billion rumored yesterday, pegging the stake at a $5 billion minority investment.

Sprint’s motivations for pursuing the Softbank tie-up likely have more to do with its heavily indebted finances than the deal’s potential to help it compete with AT&T and Verizon, Yankee Group analyst Rich Karpinski said in comments posted to the firm’s website.

“The problem with a Softbank investment in Sprint is that it doesn’t do much to directly help Sprint catch up to bigger rivals AT&T and Verizon (e.g., no new customers or spectrum in the deal), nor does it counter the improved spectrum position of a T-Mobile/MetroPCS combo,” he said.

Instead, the deal gives Sprint “a bit more financial breathing room” as it works to complete its network modernization project and recoup its $15.5 billion investment in the iPhone, he said.

“Unless Sprint wants to spend its days battling with T-Mobile for AT&T and Verizon’s mobile scraps, a Softbank deal is likely only the first domino it needs to knock over,” Karpinski said.