Clearwire in a debt offering announced on Dec. 2. As part of the offering, Sprint had the right to buy about $585 million [m] in additional debt within the next 30 days. That option expired on Jan. 2, and Sprint confirmed on Monday that it had declined to participate.

The debt offering followed . Those included layoffs of 15 percent of its staff, a delay in introducing its first branded handset, and cutbacks in certain marketing and development efforts. The company has been struggling to finance the buildout of its national WiMax network, which was scheduled to reach 120 million U.S. residents by the end of last year but fell just short of that mark, with coverage for just over 110 million.

It's not clear what triggered , but the move may have a silver lining, according to industry analysts. Eagle River Holdings, McCaw's investment company, is expected to name former Clearwire CEO Ben Wolff to replace McCaw on the board, Clearwire said last week. McCaw remains a significant investor in the company.

Wolff, who was replaced by former Vodafone executive Bill Morrow in 2009, was a strong CEO, according to analyst Monica Paolini of Senza Fili Research.

"His contribution would be more hands-on," Paolini said. "He knows the company in a more direct way, probably, than McCaw does."