Google's share of the U.S. smartphone market just keeps going up — while Microsoft's continues to decline, according to comScore. In May, Android had a 38.1 percent slice of the pie, while Windows Mobile and Windows Phone eked out just 5.8 percent, the research firm says.

On July 5, comScore released its latest tranche of highlights from its MobiLens service, involving a "nationally representative" sample of more than 30,000 U.S. mobile subscribers. For the three-month period ending in May, 234 million Americans 13 and older used mobile phones, and 78 million of them owned smartphones, the company says.

Not only was the proportion of smartphones up 11 percent from the preceding three-month period, but Google's Android ranked as the top operating system yet again. Android was up 5.1 percentage points, with 38.1 percent of U.S. smartphone subscribers, says comScore.

Apple was another gainer, though just by 1.4 percentage points, and now has 26.6 percent of the U.S. smartphone market, according to the research firm. RIM ranks third with 24.7 percent share, but declined 4.2 points, comScore adds.

Meanwhile, comScore's report didn't bring good tidings for Microsoft. Redmond's mobile operating systems, including Windows Phone 7 and Windows Mobile — according to other reports, the latter still outsells the former — were down to just 5.8 percent share.

According to comScore, Microsoft's share has been declining steadily, as follows:

• January 2011 — 8 percent
• February 2011 — 7.7 percent
• March 2011 — 7.5 percent
• April 2011 — 6.7 percent
• May 2011 — 5.8 percent

comScore didn't speculate on why Microsoft hasn't been faring well, but other researchers have pointed to a massive increase in the number of low-cost Android phones, coupled with a relative dearth of Windows Phone 7 introductions. Some have also claimed U.S. carrier promotion of Windows devices is poor, while some customers may be waiting for Microsoft's fall introduction of "Mango" updates to its mobile operating system.

comScore also reported on OEM market share, noting that Samsung ranked as the top OEM with 24.8 percent of U.S. mobile subscribers, followed by LG with 21.1 percent share and Motorola with 15.1 percent share. Apple strengthened its number-four position with 8.7 percent share of mobile subscribers (up 1.2 percentage points), while RIM rounded out the top five with 8.1 percent share.

Regarding mobile content usage, comScore says that during May, 69.5 percent of U.S. mobile subscribers used text messaging, 39.8 percent used browsers (up 1.5 percentage points), and downloaded applications were used by 38.6 percent (up 2.0 percentage points). Accessing of social networking sites or blogs increased 1.8 percentage points to 28.6 percent of mobile subscribers; game-playing was done by 26.9 percent of the mobile audience (up 2.3 percentage points); and 18.6 percent listened to music on their phones, the research firm adds.

Jonathan Angel can be reached at [email protected] and followed at www.twitter.com/gadgetsense.

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