At a time when sales of cell phones are slowing in the United States, there's one kind of mobile device that appears to be defying the trend: smartphones.

Whether you're an Apple fan or not, there's no question the company's iPhone, with a new model to be announced today, has helped contribute to the recent success of smartphones, devices that can handle e-mail and Web surfing, as well as other programs.

Lower monthly prices on phone data plans, a growing consumer interest in using the mobile Internet and a wide offering and price range of devices are all also among reasons for smartphones' success.

"Despite economic concerns, the smartphone market continued to expand in the United States, driven by heavy advertising and strong marketing promotions as more devices reached mass-market price points," Gartner analyst Hugues De La Vergne told the Associated Press recently.

Cell phone sales in general in the U.S. were down 22 percent in the first quarter this year, compared to the first quarter of 2007, according to The NPD Group.

However, smartphone sales represented 17 percent of all cell phone sales in the first quarter of 2008, up 10 percent from the same period last year, the research firm said.

Step back a bit further in time, and the smartphone trend is evident. In 2006, smartphones accounted for 5.1 percent of all mobile phones shipped in the U.S., and last year that number more than doubled, says IDC Research.

Apple’s impact on the field has been huge in a relatively short period of time. It went from zero percent of the smartphone market in the first quarter of 2007 — before the iPhone was released — to 19.2 percent in the first quarter of 2008, according to IDC.

Research In Motion, which makes the BlackBerry line of smartphones, dominates the market with a 44.5 percent share in the first quarter of this year. Apple is second, and Palm third, according to IDC Research.