MOUNTAIN VIEW, Ca. – Google Android chief Andy Rubin tweeted today that “over 500,000 Android devices” are now activated each day around the world. Moreover, he said that activations are growing at a rate of 4.4 percent week-over-week.

That figure becomes more significant when one considers that just last month at Google’s I/O Conference, the company announced that 400,000 Android devices were being activated each day, up from 300,000 daily activations in December and 100,000 activations per day a year ago.

In 2008, 400,000 to 500,000 units of the first Android smartphone, the T-Mobile G1, were expected to sell in the entire fourth quarter.

As Android’s popularity has soared, so too has its market share. According to a report released by ComScore earlier this month, Android secured 36.4 percent of the U.S. smartphone market during the first quarter of 2011, easily besting Apple’s iOS platform, which controlled 26 percent of the market. Research In Motion and Microsoft followed with 25.7 percent and 6.7 percent of the market, respectively.

On a global scale, market researcher Gartner sees good times ahead for Android handsets. The research firm said in April that it expects more than 630 million smartphones to hit store shelves in 2012 and that Android will be running on 49.2 percent of them. Apple’s iOS will come in second with 18.9 percent market share, Gartner predicts.

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