Buying an iPhone? Not so fast . . .

SAN FRANCISCO -- Apple Inc. said Monday its online stores in the U.S. and U.K. are sold out of the iPhone, a sign supplies are being winnowed ahead of the launch of the device's next generation featuring faster Internet surfing speeds.

The Cupertino-based company confirmed that the iPhone is out of stock online, but added that brick-and-mortar stores run by Apple and iPhone carriers including AT&T Inc. might still have units available. Apple has been known for clearing out its inventory of a certain product ahead of a major upgrade.

Apple spokeswoman Natalie Kerris declined to comment on reasons for the shortage and on Apple's plans for an update to the device, which is widely expected to be unveiled in June at Apple's Worldwide Developers Conference in San Francisco.

The paucity of iPhones for sale in some markets comes as Apple is hust-ling to meet its goal of selling 10 million of the hybrid iPod-cell phone-Internet surfing gadgets by the end of 2008. So far, Apple has sold 5.4 million iPhones, according to the latest data as of the end of March.

One way Apple is expanding the

iPhone's reach is by inking deals with wireless carriers around the world, even breaking its pattern of requiring exclusivity to sell in a certain country.

In recent weeks, Apple has announced partnerships to bring the

iPhone to much of the Asia-Pacific region, Latin America, Canada and more countries in Europe.

Industry observers say some people may be holding off on buying an iPhone until the much-rumored next-generation of the device is launched, and the phone is officially rolled out in more countries.

It takes technical gymnastics, but it's still possible to get the phone in some markets where Apple doesn't have arrangements with wireless carriers.

Many of the phones sold so far have been bought legitimately in one country, modified to work on any cellular network, and resold in countries where Apple doesn't have agreements to sell the iPhone. The trend expands the reach of the iPhone but deprives Apple of some of the subscriber fees that Apple splits with its carrier partners.

Another knock against the iPhone's current design is that it works over so-called 2.5G networks instead of the faster 3G, or third-generation, cell phone networks, which are popular outside the U.S. The difference in performance is similar to a dial-up Internet connection versus a high-speed broadband connection.

Apple's chief executive, Steve Jobs, has said Apple went with the slower cellular technology because the chips for 3G networks were too bulky and power-hungry when the iPhone was being designed, and because the iPhone automatically switches to faster Wi-Fi networks when they're available.

The next generation of

iPhones is expected to work over 3G networks, which makes tasks like downloading videos easier. Apple is also planning a software update for this summer that makes the

iPhone work better with corporate e-mail, a necessary upgrade to help the iPhone compete with Research in Motion Ltd.'s BlackBerry and Palm

Inc.'s Treo smart phones.

Girding for a fight with Apple in the business-oriented smart-phone space, Research In Motion on Monday unveiled the Bold, its first BlackBerry model to work over 3G, helping its shares climb to an all-time high of $143.08. The stock closed Monday up $9.20, or 6.9 percent, at $141.97.

Apple shares closed up $4.71, or 2.6 percent, at $188.16.