Investors have been treating  Clearwire as if it is pretty much dead. But the Kirkland broadband wireless company today preannounced selected third quarter results showing that wholesale subscriber growth jumped 29 percent to 1.9 million subscribers and revenues topped analysts’ estimates, coming in at $332 million.

Wall Street is responding, pushing the stock up more than 17 percent in trading this morning. That follows a very tough 30-day period in which shares of the company are still off 40 percent.

And even though the company’s wholesale subscriber count is growing — leading to an improved adjusted EBITDA loss by more than 50 percent in third quarter — some are still worried about the company’s future.

And the big question mark remains Sprint, a longtime Clearwire wholesale partner and investor which unveiled its own 4G network plans this week. Those plans, for the most part, didn’t include Clearwire.

Sid Parakh, an analyst at McAdams Wright Ragen in Seattle, wrote in a research note today that the improvement in the Clearwire’s business operations provides confidence in its ability to manage costs and conserve financial resources. But he also said that it doesn’t address what will happen after 2012, once Sprint’s deal with Clearwire concludes. Sprint represents the majority of Clearwire’s wholesale subscriber base, and if the carrier follows through with plans to build its own 4G network it may no longer need Clearwire.

Parakh writes that Clearwire doesn’t have many options beyond Sprint, and that its cash crunch could hamper an ability to jumpstart retail operations.

“Overall, we continue to think that Clearwire has significant headwinds going forward,” he writes. “While funding remains the key issue near-term, subscriber base sustenance/growth challenges come next.”

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