Piper Jaffray analyst Gene Munster has checked 20 Apple stores from across the country and he discovered quite a strange fact: the iPhone, Apple’s ultimate gadget that started a real mobile revolution, is sold out.

Munster has an explanation for this and he believes that Apple is on the verge to introduce the widely-rumored and awaited 3G iPhone.

Though the strange case of the missing iPhones could be explained by a production problem, Munster said the chances that Apple is confronted with this kind of issues are below 20 percent.

However, Dan Frommer from Silicon Alley Insider has another theory. He received an anonymous tip that the resellers are buying as many iPhones as possible. After all, China needs its own supplies of iPhones, doesn’t it?

Frommer could have a point here as in February a report from In-Stat revealed that although the iPhone never was officially launched in China, there are already 400,000 Chinese citizens that own such a phone.

Also, Bloomberg cites an Apple spokesperson who said that the stores are constantly supplied with new phones.

“We are working to replenish iPhone supplies as quickly as we can,'' Apple spokesman Steve Dowling said for Bloomberg. “Our stores continue to receive shipments almost every day.” The 3G iPhone was confirmed last year by Steve Jobs, but he didn’t indicate any time frame for the launch. Apple hopes to sell 10 million iPhones until the end of this year.

Toni Sacconaghi from Bernstein Research confirmed the lack of iPhones also, but in his opinion, Apple has a production problem.

"In our view, the most likely explanation for this unusual situation is a production shortfall, possibly due to a component shortage," analyst Toni Sacconaghi wrote in a note, quoted by Reuters.

Meanwhile, MarketWire reports that the American Technology Research analyst Shaw Wu shares Munster’s opinion that a 3G iPhone is nearing. However, unlike Munster, Shaw Wu believes that the new launch will take place in June or July.