"Clearwire can't go and market LTE without having a cell network or a strong partner," Paolini said. Analysts at the New York event challenged Sprint over the possibility of a Clearwire bankruptcy, to which CEO Dan Hesse said no wireless bankruptcy has ever left paying customers without service.

Clearwire defended its own prospects.

"Sprint remains dependent on Clearwire for 4G and nothing about today's announcement changes that," Clearwire said in a statement Friday. "Even with their re-allocation of existing spectrum, it's obvious that their spectrum resources are insufficient to meet the long-term demands of mobile data, but this is not unique to Sprint. Data capacity will clearly stress the capabilities of the low-capacity 4G deployments of other carriers due to their spectrum constraints."

For Sprint's part, the Network Vision project is impressive technologically, but it will cost far more than adding LTE to Clearwire's network and expanding its reach, Paolini said. "It doesn't make sense to have two networks," she said.

More notable yet is the fact that Clearwire has a huge amount of radio spectrum, exceeding 100MHz in most cities, yet Sprint plans to deploy LTE using the frequencies it already uses for its 3G and 2G networks. The Network Vision technology is designed for doing this gradually through software changes.