The most recent quarterly returns are in on U.S. cell phone sales, and Apple seems to have taken a big bite out of Windows' market share. And it has Research in Motion in its gun sights.

For years, Windows Mobile and Research and Motion phones dominated the cellular marketplace. But that was then and this is now. The iPhone, despite a life span of only six months, already is the second-highest selling mobile phone in the U.S.

According to the high-tech research firm Canalys, Apple's iPhone garnered 28 percent of the U.S. mobile phone 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. Apple did cut its price for the iPhone $100 during the 2007 holiday season, although Canalys doesn't say how much of an impact that had on U.S. sales (my guess is . . . plenty).

Kudos to Apple, but of course, these are just U.S. numbers. Globally, the cell phone landscape shakes out differently. Nokia, which typically dominates around the world but not in the United States, sold 52.9 percent of smartphones worldwide in the fourth quarter. Research in Motion 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 has triggered a flood of interest in U.S. cell phone use. What Canalys calls "converged-device shipments", which include smartphones and wireless handhelds, grew 222 percent in the United States during the quarter, according to the research outfit.

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.

Canalys says that cell phone providers are keen on luring 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.