The funny business of cell phones signals.

Consumer Reports says you may need a little duct tape on your iPhone 4 to guard against dropped calls.

Sound like a step backward? What about a cellphone signal that may fail in the middle of a large building?

Getty Images The new Sprint HTC Evo 4G smartphone is displayed at the International CTIA Wireless 2010 convention at the Las Vegas Convention Center March 24, 2010 in Las Vegas, Nevada. CTIA is the international association for the wireless telecommunications industry.

Some fear that is the problem with WiMAX, a form of mobile WiFi being used in 4G phones, like Sprint's HTC Evo.

One analyst estimates the company has sold 300,000 of the phones with their large screens, two cameras, and ability to play Flash videos.

The reviews rave that the Evo's internet speeds are lightning fast compared to 3G phones.

But not everywhere.

Sprint

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[S  Loading...      ()   ] is using Clearwire's

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[CLWR  Loading...      ()   ] WiMAX technology, and reviewers like David Pogue point out the limitations. The signal can be "spottier than a kennel of Dalmatians", he writes. There are apparently enough unhappy customers that someone started a web site called Clearwire Sucks.

Trent Cannon worked for Clearwire as it started up in Houston, but he left the company over what he says were concerns about the technology's viability. "The signal has tremendous difficulty passing through things like walls," he says. "WiMax won't work inside large structures like high rises, malls, and stadiums. You have a major presentation on the 4th floor of a building downtown and you need wireless internet to complete your demonstration. Hopefully, the conference room is near a window or you will need Robin William's improvisation skills." Cannon believes WiMAX will eventually give way to a competitive technology known as LTE, which

Verizon

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and

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will use in their 4G rollouts. Sprint and Clearwire have the option of eventually switching to LTE, though Clearwire says it continues to move forward with building out its WiMAX network, having recently raised almost $300 million.

"There are often differences between indoor and outdoor coverage because of how wireless signals work. That fact isn't unique to Clearwire and affects any wireless network signal," Clearwire's Mike DiGioia says. He says the company provides very detailed maps on signal strength at www.clear.com/coverage.

The company has let go its direct sales staff but says it plans to add 2,600 jobs this year. Many Clearwire products are sold through Best Buy

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[BBY  Loading...      ()   ], where a source says the chain is paid $240 for every full activation, but where one store "well within the coverage area" has had a 23 percent churn rate. "Overall it's a good service, they just need to work out the coverage," says the source. One independent salesman calls Clearwire's products "decent", adding they can provide very fast speeds when you are near a tower. "But if I'm two to three miles away, where they say I'm still covered, it's not working."

Have you bought a 4G phone or do you use WiMAX? What has your experience been? Let me know in the comments section.

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