As Sprint builds its LTE business, it will need to line up mobile devices that can use both types of networks, as well as the separate frequency bands that Sprint and Clearwire are using. The carriers will also have to work out likely teething pains in making devices go on to the best network where both are available, Paolini said. One saving grace is that the LTE networks won't be carrying voice calls, which are even more sensitive to bumpy handoffs between networks.

This may help to prime the pump for dual-technology devices in the developed world, separate from the types of products being developed for TD-LTE networks in China and India. But the deal with Sprint is especially important for Clearwire, which otherwise would have had trouble getting a lot of devices made for its own services or wholesale deals with smaller carriers, Paolini said. Clearwire has already announced a partnership with China Mobile to help build a TD-LTE ecosystem.

To keep up with demand for mobile data over the next few years, Sprint has already laid out elaborate plans for a flexible new infrastructure and a partnership with satellite-cellular startup LightSquared, all of which is separate from its Clearwire relationship. But on Wednesday, Sprint finally described a continuing role for Clearwire beyond the companies' WiMax wholesale deal, which expires at the end of next year.

The promise of a continuing revenue stream from Sprint should help Clearwire raise the funds necessary to build its LTE network, for which the company has said it needs to raise about $600 million. But analysts said it's doubtful Clearwire will be able to maintain its own branded mobile service, called Clear. The company has been cutting back marketing efforts for several years under financial constraints.

Clearwire has already spent too much money selling a mobile data service that essentially competes against its wholesale partners, said analyst Chetan Sharma, from Chetan Sharma Consulting.