Apple’s iOS was being used by one out of every three US smartphone users by the end of May 2012, according to digital measurement firm comScore’s MobiLens survey.

Apple’s iOS secured 31.9 percent of the US smartphone market by the end of May, up 1.7 percentage points compared to February, although Android continued to lead the way, accounting for 50.9 percent of smartphone subscribers (up 0.8 percentage points). RIM’s market share fell by 2 percentage points to leave it on 11.4 percent, followed by Windows Phone with 4 percent (up 0.1 percentage points) and Symbian with 1.1 percent (down 0.4 percentage points).

Samsung was the top mobile handset manufacturer (for smartphones and feature phones) in the US, increasing its market share by 0.1 percentage points to hit 25.7 percent while LG was second with 19.1 percent. Apple ranked third with 15 percent, up 1.5 percentage points, followed by Motorola (12 percent) and HTC (6.1 percent).

In May, downloaded apps were used by 51.1 percent of mobile subscribers (up 1.6 percentage points) with browsers being used by 49.8 percent, up 0.6 percentage points. A third of users (33.5 percent) played games on their mobile devices and 27 percent listened to music.

The research, which covered 30,000 US mobile subscribers, suggested that out of the 234 million Americans aged 13 years or older using mobile devices, almost 110 million own smartphones – a 5 percent increase compared to February.