Clearwire downplayed increasing Wall Street concerns about its growth prospects during a conference call Wednesday following the release of its first-quarter results.

The Kirkland-based company, led by wireless entrepreneur Craig McCaw, will need a ton of money to rapidly build a U.S. network based on an emerging wireless broadband technology called WiMax.

The quarterly results marked the first time Clearwire released figures since raising $600 million in a public offering in March.

The company used Wednesday's call with the investment community as an opportunity to emphasize that all its significant numbers grew — revenues, subscribers and losses — and that its 25 oldest markets were performing well.

But it also focused on explaining how it plans to balance growth with cash reserves. Analysts' fear that the money-losing company will need billions more to complete the network has contributed to a decline in Clearwire's stock price since it debuted.

The company estimates it will need $1.6 billion more than the $1.5 billion in cash and short-term investments it has on hand. Since its inception, Clearwire has raised $2 billion in capital.

Chief Executive Ben Wolff said the company plans to be able to reach up to 125 million customers in the next five years (up from 10 million today), but can scale back to reach profitability sooner.

John Butler, Clearwire's chief financial officer, said the plan can be tweaked to match the funds the company raises, but that shareholders should realistically count on higher expenses and losses for some time as Clearwire makes large investments in equipment.

In the first quarter, the company lost $92.6 million, or 64 cents a share, on revenues of $29.3 million. A year earlier, it lost $55.3 million, or 73 cents a share, on revenues of $22.7 million.

Jonathan Schildkraut, an analyst with Jefferies & Company, which does banking business with Clearwire, said the company did a good job explaining how it expects to control its growth.

"For the first time I heard them say they could slow down the pace of the rollout to meet whatever kind of fundraising they saw," he said. "They basically were saying, 'We are smart people. We aren't building for the sake of building. We can cool down in order to match our cash consumption to what is readily available.' "

The company reported it added about 52,000 subscribers during the first three months of 2007 to bring the total to 258,000. It also reported fairly low customer turnover, known as "churn" in the industry, of 1.6 percent.

In the 25 markets where it first rolled out service, Clearwire on average was servicing 10.4 percent of the households. And, as it added customers in those markets, expenses were spread over a larger customer base, allowing gross margins to increase to 72 percent in the first quarter from 48 percent in the same period a year ago.

"What we are most excited about is that we demonstrated real success in our core markets," Wolff said. "As you are investing and building networks, they are capital intensive, so the fact that we are quote 'losing money' shouldn't be a surprise."

Tricia Duryee: 206-464-3283 or tduryee@seattletimes.com