Clearwire (NSDQ: CLWR), the company that just announced a massive plan to merge with Sprint (NYSE: S) Nextel’s WiMax division, reported Q1 results today, saying that compared to the year ago period, subscribers grew 72 percent and revenues grew 76 percent. Clearwire was obviously distracted in the first quarter as it negotiated with Sprint and investors, and said it did not add any new markets in the first quarter of 2008. The reason: the company said it is focused on improving operating efficiency and profitability in its current markets, while also working on rolling out its first mobile WiMax market, expected later this year. The company’s stock had been increasing based on rumors that a deal with Sprint might close soon, but after the $14.5 billion deal was completed (which included an investment of $3.2 billion from Comcast (NSDQ: CMCSA), Time Warner (NYSE: TWX) Cable, Bright House Cable, Intel (NSDQ: INTC) and Google), the stock tanked, trading at $12.75 a share today.

Release. Webcast. You can find our coverage of Sprint, which also released Q1 earnings today, here.

Highlights from the call after the jump…

Financial highlights:

-- Q1 revenues jumped 76 percent to $51.5 million with average revenue per user standing at $36.86, increasing slightly compared to the year ago period because of increased sales of new services, including VoIP and PC cards.

-- The company lost $176 million, or $1.08 a share in Q1 compared to a loss of $92.6 million, or 64 cents a share in the same period a year ago. Analysts had been expecting a loss of 99 cents a share.

-- Subscribers in Q1 grew by 48,000, which was slightly less than the 52,000 added in the year ago period. Total subscribers at the end of Q1 totaled 443,000, a 72 percent increase over Q1 2007. Churn, or the rate at which customers were leaving, was 2.2 percent, increasing from the year ago period of 1.6 percent.

-- Cost per Gross Addition is also up in Q1 compared to the same period a year ago. It cost $393 to acquire each subscriber in Q1, increasing from $343 last year.

-- The company likes to look at some of its earliest markets to determine how well wireless broadband is performing. It said nearly 60 percent of the company’s 46 U.S. markets are EBITDA positive at the end of Q1, and several markets are exceeding 30 percent EBITDA margins. “We are encouraged by the fact that we are achieving these margins well before we launch our mobile WiMax services,” said CEO Ben Wolff.

Highlights from the call:

-- Portland trial: It’s on schedule, with the 145 square mile coverage area being converted over to a production network as the company prepares for commercial launch. Additionally, it’s developing additional sites to cover the remainder of the city to soft launch later this year. Three additional mobile WiMax networks will be Atlanta, Las Vegas, and Grand Rapids, each of which would cover different demographics, landscapes and topographies.

-- Devices: Clearwire said it’s device roadmap is quite healthy for upcoming mobile WiMax devices. It’s working on residential modems, USB dongles and express cards. It’s also starting to test Intel-based WiMax embedded laptops, and Nokia’s (NYSE: NOK) n810 Internet Tablet WiMax edition.

-- Market: Expect to be able to reach 120-140 million by end of 2010 and 60 to 80 million by the end of 2009.

-- Mobile WiMax vs. LTE: CTO John Saw said that WiMax took about three years to develop between ratification of the standard to production, calling it “the fastest ramp of a wireless technology” he’s seen. “It will be interesting to if LTE can keep up with the three-year cycle. In addition to any kinks operators may encounter along the way, prospective LTE operators will have to solve significant challenges,” including backhaul. “LTE will need much more than a couple of T1 lines, and if you think LTE is a simple upgrade, it’s not.” Most 2G and 3G cell sites won’t be upgradeable without using a forklift, and some spectrum may have to be reused, he added.

-- Subscribers: Expects to achieve 510,000 subscribers on the low-end by the end of 2008. The company is seeing some softness in the economy, and increased its credit requirements at the end of 2007.

-- iPCS lawsuit: A lawsuit filed earlier today by iPCS claims that the Clearwire-Sprint Nextel JV breaks an agreement that it has with Sprint. CEO Ben Wolff said: “We don’t anticipate it affecting the time of close or the ability to close the transaction.”

-- JV response: In response to a question on whether more device companies or MVNOs became interested in the company since last week, Wolff said: “It has sparked a lot of interest among parties we’ve been in discussion with and parties we had not been in discussions with—but certainly we’ve gotten a lot of interest.”