Apple’s 3G iPhone was the best-selling handset in the U.S. during the third quarter of 2008, according to data compiled by The NPD Group. Apple had previously reported that it sold about 6.89 million iPhones (3G) in the quarter. The research group identifies Apple’s new device “as the leading handset purchased by adult consumers in the U.S.”

It beat out Motorola’s RZR V3 (all models), RIM’s Blackberry Curve, the LG Rumor and the LG enV2, the Port Washington, N.Y.-based research group said. RAZR was ranked as the top seller for past 12 quarters. That is bad news for Motorola (s MOTO), which is already on the mat after being pummeled with losses and declining market share. Funnily enough, phones with a QWERTY keyboard were in high demand — 30 percent of the handsets sold in this quarter had keyboards, versus just 11 percent the year prior. According to NPD Group, the domestic handset purchases by adult consumers declined 15 percent year over year in third quarter to 32 million units. Consumer handset sales revenue fell 10 percent to $2.9 billion.