Smartphones now account for one-third of the mobile Internet traffic worldwide, up from 26 percent six months ago, with the Apple iPhone leading the way, according to a report released last week by the mobile ad company AdMob.

The report, which found the iPhone responsible for 33 percent of smartphone traffic worldwide and 50 percent stateside, is based on AdMob's tracking of ads it serves ads for 6,000 Web sites and 1,000 applications globally. The company's ad server tracks every time an ad is requested on a device and uses the data to determine what phones and mobile operating systems are the most popular.

Following Apple's iPhone, the top mobile traffic producers worldwide are the Nokia N70, BlackBerry 8300, Nokia N80, and Nokia N73, AdMob found.

In the U.S., the iPhone is followed by Research in Motion's (RIM) BlackBerry Curve, BlackBerry Pearl, Palm Centro, and HTC Dream (also known as the Android-based T-Mobile G1). Combined, the devices accounted for 77 percent of mobile traffic in February, according to AdMob's February Metrics Report.

The news comes at a time when the smartphone market is heating up, with sales pegged to grow, albeit at a slower rate, over the next five years.

The real success story here, though, may be that Google's mobile open source platform Android rose to account for 5 percent of all U.S. traffic within just three months after launching with HTC's T-Mobile G1.

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