Apple Inc.’s iOS and Google Inc.’s Android mobile platform have been steadily gaining ground on the leading smartphone platform, Research in Motion’s BlackBerry. Now one of those challengers has overtaken BlackBerry and the smartphone platform champion is Android, according to web and mobile web measurement firm comScore Inc.

For the three months ending in January, Android captured 31.2% of smartphone market share, RIM’s BlackBerry ranked second with 30.4% and Apple’s iOS came in third with 24.7%. Microsoft and Palm rounded out the top five with 8% and 3.2% respectively.

65.8 million U.S. consumers owned smartphones during the three months ending in January 2011, up 8% from the preceding three-month period, comScore reports.

Text messaging is still the most popular activity on a mobile device, comScore says. In January, 68.1% of U.S. mobile subscribers used text messaging, unchanged from three months earlier. But mobile browsing and app downloading, most often associated with smartphones, are gaining traction. 37% percent of U.S. mobile subscribers used a mobile browser up 0.8 percentage points from the three months ending in October and 35.3% downloaded apps, up 1.6 percentage points, comScore reports. Accessing social networking sites or blogs via mobile increased 1.1 percentage points to reach 25.3% of mobile subscribers, playing games held steady at 23.7% and  listening to music rose 1.1 percentage points to reach 16.5% of subscribers.