Once the poster boy for WiMAX, a 4G wireless technology thought to be the heir apparent to cellular, Clearwire (NASDAQ: CLWR) is once more under Sprint Nextel's (NYSE:S) thumb.

According to this Securities and Exchange Commission filing, Sprint has agreed to purchase more than 30 million Class A and B shares of Clearwire, bringing its overall ownership interest up to 50.8%. Comcast (NASDAQ: CMCSA) and Intel (NASDAQ:INTC) remain as minority shareholders.

Craig McCaw founded Clearwire in 2004, a decade after selling a pioneering cellular venture to AT&T (NYSE:T) for $11.5 billion. He isn't making out nearly so well with Clearwire. According to the filing, Sprint is paying about $100 million for the bulk of McCaw's remaining interests, most of which are held by his investment company, Eagle River Holdings.

In selling, McCaw is at least tacitly conceding that Clearwire failed at becoming the disruptor he once thought it could be. "It really is about making the world a better place ... We think we can be a small part of that," he said in a speech at the CITA trade show in 2004, shortly after the company's founding.

A grand ambition, to be sure, but one that's gone unrealized. AT&T and Verizon's (NYSE:VZ) wireless group have rolled out LTE networks to fill the gap that Clearwire had sought to occupy with WiMAX. Sprint isn't in any hurry to resuscitate the technology.

Fortunately, it doesn't have to: Clearwire, blessed with a huge inventory of excess spectrum, is overlaying its existing WiMAX network with a protocol called TD-LTE that should play nicely with Sprint's own LTE network, which promises users unlimited 4G data usage for a fee.