Morrow cited personal reasons for resigning from both the CEO post and Clearwire's board of directors, the company said on Thursday. He will serve as an adviser during the transition to a new CEO, Clearwire said. The company has formed a search committee, led by board member Dennis Hersch, to find Morrow's permanent replacement. Stanton, the interim CEO, has been chairman of Clearwire since January but on the company's board since 2008.

Also on Thursday, Clearwire announced that Chief Commercial Officer Mike Sievert and CIO Kevin Hart are leaving the company to pursue other opportunities.

Chief Financial Officer Erik Prusch has been promoted to the newly created position of chief operating officer, and Senior Vice President and Treasurer Hope Cochran has been promoted to CFO, Clearwire said.

The company has built out a WiMax network that now reaches more than 110 million U.S. residents, but it faces financial challenges as well as growing competition and a sometimes awkward relationship with its majority owner, Sprint Nextel. Last October, Clearwire announced it would cut 15 percent of its staff and delay the introduction of its first branded smartphone, among other steps, in order to conserve resources.

Clearwire was the first significant carrier to offer a next-generation high-speed mobile service when it was launched as a joint venture involving Sprint, Comcast and other partners in 2008. It now faces a fast mobile data network from Verizon Wireless, using LTE (Long-Term Evolution) technology, which AT&T also plans to roll out.