Microsoft and Palm are losing market share to devices based on Google’s Android operating system, according to January metrics compiled by comScore.

The firm reports that the U.S. smartphone market share of Microsoft’s Windows Mobile devices lost 4 percentage points in January, falling to 15.7 percent from 19.7 percent in October. Palm’s market share dropped 2.1 percentage points, to 5.7 percent.

Meanwhile, Google’s market share of its Android devices more than doubled to 7.1 percent in January, making it the fastest-growing smartphone OS in the U.S. market.

Research In Motion’s BlackBerry devices gained 1.7 percentage points, outpacing growth of Apple’s iPhone, which gained less than a half of a percentage point.

Overall subscriber figures for non-smartphone categories remained fairly stable, with Motorola losing 1.2 percentage points of market share and Research In Motion gaining 1.4 percentage points.

ComScore also reported that mobile content usage grew across all categories, from listening to music on a device to sending text messages. About 17 percent of subscribers accessed a social networking site or blog from their handsets in January, up from 13.8 percent in October. Usage of mobile browsers, apps, text messaging and music also posted strong gains.