The question, though, is whether Clearwire has enough spectrum to launch a truly nationwide network.

"I just don't think they have [enough spectrum], even with the spectrum they just acquired," Roberts said.

The doubters

Sprint claims that its mobile WiMax network will give users typical download speeds of between 2 Mbit/sec. and 4 Mbit/sec. and typical upload speeds of about 1 Mbit/sec. That's at least several times faster than the speeds promised by the next generation of 3G service to which the cellular carriers, including Sprint, are currently upgrading.

Kerton, however, said there are many more doubts about mobile WiMax's technical capabilities than proponents let on.