Next-generation wireless network provider Clearwire (NASDAQ:CLWR) just reported weak second-quarter results. Sales rose 9% over the 2008 period to stop at $63.4 million. Last year's net loss of $0.40 per diluted share shrunk slightly to $0.38 per share. However, for a company like Clearwire that’s building out an expensive network and is focused on growth, investors were focused mainly on the disappointing revenue and subscriber growth.

Clearwire added 12,000 net new customers this quarter for a grand total of 511,000 accounts, an 11% annual improvement. The company is building out long-range WiMAX broadband services as fast as it can, but the new WiMAX subscribers can in many cases simply upgrade from older and slower Clearwire services rather than converting from traditional wireless carriers like AT&T (NYSE:T) and Verizon (NYSE:VZ) Wireless or landline-based broadband connections. That puts a crimp in Clearwire's growth rates.

The company is using funding from technology heavyweights like Google (NASDAQ:GOOG), Intel (NASDAQ:INTC), and Sprint Nextel (NYSE:S) to build network stations across the country. By the end of 2009, Clearwire should be able to sell high-speed Internet services to 30 million potential customers from Honolulu to Baltimore. One year after that, the company targets 120 million American customers.

Converting a large coverage area into actual customers will take a serious marketing blitz. It's not enough simply to build out great technology services and hope for the best. Verizon's FiOS service, which brings TV and Internet services to customers over ultra-fast fiber-optic networks, currently reaches 13.8 million households -- but only has 2.5 million subscribers. And that's with a heavy, heavy marketing push over the last couple of years.

In other words, you should expect Clearwire to grow, but it'll be slow going at first. WiMAX is currently only good for piping Internet traffic to your laptop or netbook. Once handset makers like Motorola (NYSE:MOT) start building WiMAX reception into their smartphones, Clearwire's customer count should take off with a big bang. But that moment could be years away.

This stock has more than doubled over the last six months, even after today's 15% haircut. Clearwire is not profitable, and won't be for years. There's no telling how Mr. Market will treat this puppy until we've seen the WiMAX service gain some traction. Until then, I believe your portfolio would be better off with a traditional telecom stock like Verizon or AT&T. But I’d love to hear what the Foolish community thinks as well. Which wireless stock would you buy today? Let us know in the comments!

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Fool contributor Anders Bylund owns shares in Google, but he holds no other position in any of the companies discussed here. You can check out Anders' holdings or a concise bio if you like, and The Motley Fool is investors writing for investors.