According to market research firm NPD Group, AT&T is reaping big rewards from its exclusive iPhone deal with Apple. NPD says that its research has concluded that one in three iPhone 3G buyers came to AT&T from another provider specifically to get the iPhone 3G.

NPD also says that its research shows the iPhone 3G is the second best-selling handset among consumers in the US behind the Motorola RAZR V3. Before the launch of the 3G iPhone the original iPhone counted for 11% of the consumer smartphone market, after the 3G the iPhone held 17% of the market. In June through August 2008 the iPhone 3G was the best selling smartphone.

“The launch of the lower-priced iPhone 3G was a boon to overall consumer smartphone sales,” according to 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.”

Via NPD Group