Clearwire (NSDQ: CLWR), which is waiting for regulatory approval of its merger with Sprint’s (NYSE: S) WiMax division, announced second-quarter results today, saying that its initial markets are performing well, but that it didn’t add very many new subscribers during the quarter as it focuses on profitability and upgrading its network to mobile WiMax. It said it added as few as 18,400 new subscribers, down from adding 41,000 subscribers a year ago. It ended the quarter with 461,000 total subscribers, and said it doesn’t expect to add a material amount of subscribers in the second-half of the year.

Still, Clearwire recorded revenues of $58.6 million in the quarter to beat Wall Street expectations of $54.2 million. Clearwire’s net loss widened to $199.1 million in the second quarter from $118.1 million in the same period in 2007. In after hours trading, the company’s stock was up about 10 cents to $9 a share.

Release. Earnings Call.

Other highlights:

Initial markets: The company likes to report separate results for its markets that have been around the longest to demonstrate the viability of the business. For the initial markets, it said it has a record Market EBITDA margin of 34 percent. A number of the 25 markets are now exceeding 40 percent EBITDA margins, and some are approaching 50 percent.

On true WiMax: Currently, it’s first beta trial of mobile WiMAX technology is taking place in Portland, Ore., and the company is focused on accelerating the upgrade of our existing U.S. markets to mobile WiMAX technology. The closing the Sprint transaction will influence the launch of Clearwire’s first four mobile WiMAX markets. When it launches its first four WiMAX markets Clearwire expects to have approximately 22 million covered POPs, up from 16.8 million.

On the merger: Still expects a fourth-quarter close. At that time, it will have significant spectrum resources, and will receive $3.2 billion in capital from our its investor group, which includes Intel (NSDQ: INTC), Google (NSDQ: GOOG) and cable companies, such as Comcast (NSDQ: CMCSA) and Time Warner (NYSE: TWX).

Outlook: Clearwire affirms its 2008 revenue targets of $205 million to $215 million. With the focus on upgrading existing markets to mobile WiMAX, the company does not expect to add materially to its total number of subscribers during the second half of 2008.