The company's revenue soared to US$242 million from $106 million a year earlier, as its subscriber base grew to about 6.15 million, counting both users of its own WiMax service and those who access the network via Sprint Nextel, Comcast and other partners.

After the quarter ended, Clearwire reached an agreement with Sprint Nextel in which for its customers' use of the WiMax network. Because the deal is retroactive, it includes a $16.1 million payment for the first quarter, which will be added to Clearwire's revenue.

Clearwire, majority owned by Sprint, got a head start on building a so-called 4G (fourth-generation) mobile data network before Verizon launched its LTE (Long-Term Evolution) infrastructure late last year and ahead of AT&T's planned LTE deployment coming this year. But it has struggled to fund the massive cost of building a brand-new network and last year was forced to cut back retail sales efforts under its own brand.

In the first quarter ended March 31, Clearwire posted a net loss of about $227 million, or $0.93 per share. But it expects to achieve positive EBITDA (earnings before interest, taxes, depreciation and amortization) in 2012. The company said it has enough cash and investments to continue operating for at least the next 12 months.

"We grew rapidly, and we substantially cut costs," Chairman and Interim CEO John Stanton said on a conference call to discuss the results.