Google's (NASDAQ:GOOG) Android operating system rose to 39 percent U.S. market share through June, up from 38 percent in May, according to Nielsen.
Apple's iOS-based iPhone is still in second place, but rose to 28 percent from 27 percent in May and 26 percent in April.
While Android leads by dint of massive exposure across multiple OEMs selling handsets in the United States and all over the world, Apple remains the top smartphone maker in the United States with that 28 percent share.
HTC is No. 2 with 20 percent in the United States, including 14 percent of Android phones and 6 percent of Windows Mobile/Windows Phone 7 gadgets.
Motorola is No. 3 with 11 percent of all Android phones. Samsung follows at a total of 10 percent U.S. share, with 8 percent of Android phone sales and 2 percent of Windows Mobile/WP7 sales.
In other Nielsen smartphone market share updates, Research In Motion's (NASDAQ:RIMM) BlackBerry continued to lose share for June, accounting for 20 percent share. That's down from 21 percent in May and 23 percent in April.
Smartphones based on Microsoft's Windows Mobile and Windows Phone 7 accounted for 9 percent of the U.S. market as the company continues its gradual transition of replacing Windows Mobile in favor of WP7.
The company just shipped its WP7 "Mango" version, which is well regarded by reviewers, to manufacturing. Mango phones will hit the market en masse this fall.
For now, though, the smartphone market features two faster horses at the top: Android and iOS. There are two forthcoming events that could shape the future market share of both platforms this fall.
First, Samsung is expected to launch its well-regarded Galaxy S II smartphones, which sold 5 million units in a few countries, through AT&T and Verizon Wireless in the United States this August.
Second, Apple is expected to launch its iPhone 5 in September or October. The device should be faster, feature better cameras and could feature a virtual assistant and facial recognition perks.
Samsung needs to have a good U.S. launch in order for Android to continue its momentum; Apple's iPhone must do the same for iOS.