By Sam Oliver

Published: 11:35 AM EST

In a little over a year, Apple's iPhone has grown to become the second best-selling mobile handset in the United States, according to NPD.

A report issued by the market research firm Monday claims the touch-screen handset now trails only Motorola's RAZR V3 on the US sales charts. It also cited a surge in sales immediately following the introduction of the iPhone 3G that has helped the device garner a 17 percent share of the overall US smartphone market.

More specifically, NPD said the iPhone 3G was the No. 1 US smartphone based on units sales from June through August, outselling the Blackberry Curve, Blackberry Pearl, and Palm Centro.

Of those customers who purchased an iPhone during those months, 30 percent switched from other mobile carriers to join AT&T, according to the firm. That compares to 23 percent of consumers who switched carriers during the same time period for other reasons.

Nearly half of iPhone switchers (47 percent) made the jump to AT&T from rival Verizon Wireless, while 24 percent switched from T-Mobile. Another 19 percent are reported to have switched from Sprint.

"The launch of the lower-priced iPhone 3G was a boon to overall consumer smartphone sales," said Ross Rubin, director of industry analysis for The NPD Group. "While the original iPhone also helped win customers for AT&T, the faster network speeds of the iPhone 3G has proven more appealing to customers that already had access to a 3G network."

The average price of a smartphone sold between June and August was reportedly $174, down 26 percent from the average $236 price tag during the same period last year.

Also on Monday, two independent Apple analysts issued a report suggesting that Apple has more than surpassed its self-imposed goal of selling more than 10 million iPhones during the 2008 calendar year.