ComScore yesterday released second-quarter numbers that showed two out of five smartphone users in the United States are using Google’s Android platform, while Samsung took the crown as the top smartphone OEM here.

The study surveyed more than 30,000 U.S. mobile subscribers and found Samsung to be the top handset manufacturer overall with 25.3 percent market share. Android continued to gain ground in the smartphone market, reaching 40.1 percent market share in June.

Apple strengthened its position as fourth largest OEM, with 8.9 percent share of mobile subscribers (up 1 percent), while Research In Motion (RIM) rounded out the top five with 7.9 percent share.

In the second quarter, 78.5 million people in the U.S. owned smartphones, up 8 percent from the preceding three-month period. Android penetration was up 5.4 percentage points, while Apple strengthened its No. 2 position with 26.6 percent of the smartphone market, up 1.1 percentage points from the prior period.

RIM ranked third with 23.4 percent share, followed by Microsoft (5.8 percent) and Symbian (2 percent).

So what are people doing on their smartphones? In June, 69.6 percent of U.S. mobile subscribers used text messaging on their mobile device, up 1 percent. Browsers were used by 40.1 percent of subscribers (up 1.5 percent), while downloaded applications were used by 39.5 percent (up 2.2 percent). Accessing of social networking sites or blogs increased 1.8 percentage points to 29.1 percent of mobile subscribers. Game-playing was done by 26.9 percent of the mobile audience (up 1.2 percent), while 19.0 percent listened to music on their phones (up 1.1 percent).