Samsung is the top OEM in the United States, and Android continues to grab market share on the platform side of things, according to ComScore’s MobiLens report released today.

For the three-month average period ending in April, 234 million Americans ages 13 and older used mobile devices. Samsung ranked as the top OEM with 24.5 percent of U.S. mobile subscribers, followed by LG with 20.9 percent share and Motorola with 15.6 percent share. Apple jumped to the No. 4 position with 8.3 percent share of mobile subscribers (up 1.3 percentage points), while RIM rounded out the top five with 8.2 percent share.

ComScore pegs the number of smartphone users in the U.S. at 74.6 million, up 13 percent from the three-month period ending in January 2011. Google’s Android continued it reign as the top ranking operating system with 36.4 percent of U.S. smartphone subscribers, up 5.2 percentage points. Apple also gained share, capturing the No. 2 position with 26 percent of the smartphone market. RIM ranked third with 25.7 percent share, followed by Microsoft (6.7 percent) and Palm (2.6 percent).

The report also took a look at what users were doing on their phones. Fully 68.8 percent of U.S. mobile subscribers used text messaging on their mobile device. Browsers were used by 39.1 percent of subscribers (up 2.1 percentage points), while downloaded applications were used by 37.8 percent (up 2.4 percentage points).

Accessing of social networking sites or blogs increased 2.7 percentage points, representing 28 percent of mobile subscribers. Playing games comprised 26.2 percent of the mobile audience (up 2.5 percentage points), while listening to music represented 18 percent.

MobiLens data is derived from an online survey of a nationally representative sample of mobile subscribers ages 13 and above. Data on mobile phone usage refers to a respondent’s primary mobile phone and does not include data related to a respondent’s secondary device.