Google continued to build on its lead in the U.S. smartphone market as Android increased its share to 51% in the first quarter, up from 47.3% at the end of 2011. According to the latest comScore data, Apple’s iOS grew its share by 1.1 percentage points to 30.7% while RIM dropped another 3.7 points to 12.3%. Microsoft also continued to lose ground, with the Windows Phone falling to 3.9% from 4.7% three months ago. Symbian was flat at 1.4%.

When it came to mobile activities, about half of U.S. mobile users used downloaded apps (50%) and used a browser (49.3%), up from about 47.5% each in the fourth quarter of 2011. More than a third (36.1%) accessed a social networking site or blog, 32.6% played a game and 25.3% listened to music on mobile devices. Text messaging as ever was the most common mobile activity, with nearly three-quarters (74.3%) of mobile users doing so.

Among manufacturers, Samsung was again the top brand, with 26% market share, followed by LG (19.3%), Apple (14%), Motorola (12.8%), and HTC (6%). Apple saw the biggest gain, increasing its slice of the handset market by 1.4 percentage points.