Sprint's troubles are only one reason why it is willing to gamble on mobile WiMax. Another is that the company was ordered by the FCC to either use the enormous amount of valuable WiMax-appropriate spectrum it acquired along with Nextel in 2005 or to give it up. If it gives up the spectrum, Sprint's more powerful competitors could eventually acquire it.

"Sprint is in a very unique spectrum position," said Mike Roberts, a principal analyst at Informa Telecoms & Media, a London-based industry analyst group. "It's either use [the spectrum] or lose it."

Even skeptics like Kerton agree that Sprint's gamble is worthwhile.

"I admire Sprint's bravado," Kerton said. "It's gutsy, and if they can succeed, they'll have an unmatchable advantage."

Clearwire's intentions are not as well known. A spokesman for the company did not return calls for this story. But two things are known: Clearwire is in the process of raising even more money via an initial public offering, and it is run by Craig McCaw, a cellular pioneer who started the company that later became the original AT&T Wireless, which was acquired by Cingular several years ago.