Clearwire, which is building a nationwide WiMax network in the U.S., announced today that John Stanton will serve as interim CEO, replacing William Morrow, who resigned from the position and the company's board of directors.

Stanton is currently Clearwire's chairman of the board. Stanton is well-known in the wireless world having served as CEO of Western Wireless, which was acquired by Alltel in 2005 and is now part of Verizon Wireless. And he worked at VoiceStream Wireless, which was sold to Deutsche Telekom to form T-Mobile USA.

In addition to Morrow, Chief Commercial Officer Mike Sievert and Chief Information Officer Kevin Hart are leaving the company. Sievert formerly worked at Microsoft and AT&T Wireless.

Clearwire said it will promote its chief financial officer, Erik Prusch, to chief operating officer. And Hope Cochran, senior vice president and treasurer, will be promoted to CFO.

The company said that Morrow resigned due to "personal reasons," but it would not elaborate. He is expected to continue to serve as an adviser to Clearwire as it looks for a permanent CEO.

"I would like to commend Bill for his tremendous leadership in building the first U.S. 4G network, adding more than 5 million subscribers, and raising funds in a challenging economic environment," Stanton, said in a press release. "Bill built a strong leadership team which enables us to promote Erik Prusch and Hope Cochran to new roles. Together, the entire management team at Clearwire remains focused on delivering value to its customers and shareholders."

Clearwire partnered with Sprint Nextel and a few other companies in 2008 to build a nationwide 4G WiMax network. Sprint Nextel resells the service to its customers as a "4G" wireless service. Cable companies Comcast and Time Warner Cable are also investors in Clearwire, and they also resell the WiMax service. Intel and Google have invested in the company as well.

Clearwire has been burning through cash as it builds the nationwide network, and in November it said it needed more investment to make it through 2011. The company tightened its belt and laid off workers. Despite growing revenue and increasing subscribers, Clearwire reported last month that fourth-quarter losses widened as expenses ballooned.

The company has been considering selling some excess spectrum to raise more cash. It's also been rumored that the company could be sold to another wireless carrier, such as T-Mobile USA.

The company has also been in a dispute with its key partner Sprint over wholesale pricing. In the press release today, Clearwire said the management shake-up is "not expected to impact the company's progress on an agreement with Sprint to resolve wholesale pricing disputes. Clearwire believes that an agreement with Sprint is imminent."

Clearwire's network is available to more than 120 million people in more than 60 markets. And even though it's been growing its subscriber base, it's facing stiff competition from other network providers, such as Verizon Wireless, which launched its LTE-based 4G wireless network in December. The competition is only expected to intensify as AT&T and T-Mobile USA continue to upgrade their networks to HSPA+, a technology that these carriers claim provides similar speeds to Clearwire's WiMax service. AT&T is also expected to launch its LTE network this summer, which will increase network speeds even more.