Even after being on the market for less than half a year, more iPhones sold in the fourth quarter than Windows Mobile phones in the United States, according to research from Canalys.

Canalys researchers estimate that the iPhone had 28 percent of the U.S. converged-device market in the fourth quarter of 2007. Research in Motion, with 41 percent, had the largest share of the market. Windows Mobile phones had a 21 percent share of devices sold in the quarter, falling into third place behind Apple.

Worldwide, the lineup is a bit different. Nokia, which typically dominates around the world but not in the United States, sold 52.9 percent of smartphones worldwide in the fourth quarter. RIM grew its share of converged-device sales to 11.4 percent, up 121 percent over the same quarter in 2006. Despite its limited availability around the world, Apple took third place with 6.5 percent of the market, just barely squeaking ahead of struggling Motorola.

Apple may have stirred renewed interest in smartphones in the United States. Converged-device shipments, which include smartphones and wireless handhelds, grew 222 percent in the United States during the quarter, according to Canalys.

The iPhone also did well in the Europe, Middle East, and Africa region, where it became available in three countries partway into the quarter. In the region, Apple came in fifth place behind Nokia, RIM, HTC, and Motorola, but beat out Sony Ericsson, Samsung, and Palm, Canalys said.

Apple's success as a new entrant is striking, but it will face challenges to keep its momentum going, said Canalys analyst Pete Cunningham in a statement. Historically, vendors with just one smartphone design, no matter how good, struggle, he said. That means Apple will have to create and refresh a portfolio of devices if it wants to increase its market share, he said.

Beyond hardware, competition is continuing in the mobile operating system market. Worldwide Symbian, which credits most sales to Nokia, had 65 percent of the market, followed by Microsoft at 12 percent and RIM at 11 percent, for the fourth quarter, Canalys said.

Despite all the buzz around mobile Linux, total Linux phone shipments in 2007 were essentially flat compared to 2006, Canalys found. In Asia Pacific, Motorola had a drop of 28 percent in its Linux smartphone shipments compared to 2006.

Phone makers are trying to attract customers to smartphones, which carry a higher price tag than low-end feature phones. However, converged devices made up just 10 percent of the global phone market in 2007, the researchers found.