Android continued on its warpath this past quarter, once again showing gains as it retained its position as top smartphone platform in the United States. Nielsen on Thursday issued its second-quarter smartphone market share data for the U.S., and Android finds itself atop the list again with 39% of the market. IOS remains in the No. 2 spot with 28% and RIM slid to 20% in the second quarter. Windows Mobile and Windows Phone combined to take 9% of the market, while webOS and Palm OS combined to account for just 2% of the market. Nokia’s Symbian OS also held a 2% share in the June quarter. On the list of top vendors last quarter, Apple held its lead by a wide margin with 28% of the total U.S. market. HTC devices accounted for 14% of Android market and 6% of the Windows Phone/Windows Mobile market, making it the nation’s top vendor in both categories and No. 2 overall. Samsung owned 8% of the Android market and 2% of the Windows Phone/Windows Mobile market in the U.S. last quarter, while Motorola topped Samsung’s Android share with 11% to slide into the No. 2 spot among Android device manufacturers.