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Gartner last year said Android wouldn’t be the No. 2 operating system in the world until 2012, but the future seems to have come early for the platform, which Gartner said today grabbed 25.5 percent of the smartphone market in the third quarter, up from 3.5 percent a year ago, good enough to move into second place behind Symbian.

The ascent of Android is well documented, and shouldn’t come as much of a surprise if you’ve been watching sales over the last year. But what it suggests is that the smartphone market is still very fluid and even predictions made a year ago are proving to be wrong. We look at the momentum of Android and Apple (s appl) and presume it to be a two-horse race, but the fact is that the competition is still in its early stages. Gartner said smartphones, which almost doubled in growth in the third quarter, only account for 19.3 percent of all cell phones sold in the third quarter, meaning there’s a lot of opportunity left as consumers make the shift to full-featured handsets.

Research in Motion (s rimm), Nokia (s nok) and Microsoft (s msft), the whipping boys of the last year, are in the process of turning themselves around, and while it’s tempting to write them off, the fact is there’s a lot of game left to play. Android’s rise just shows that it has the momentum now, as it continues to proliferate on more and more handsets on networks around the world. But seeing how fast things are changing makes me realize that picking winners at this point doesn’t make much sense. For now, here’s a snapshot of how things stacked up in the third quarter:

Android devices collectively sold 20.5 million units, up from 1.4 million a year ago, and pushed past Research in Motion. While Android surged, iOS held its ground, dropping slightly from 17.1 percent to 16.7 percent in the third quarter. Apple devices sales overall have almost doubled, from 7 million units last year to 13.5 million in the third quarter. Research in Motion, meanwhile, dropped to fourth place with a 14.8 percent market share, down from 20.7 percent in the same quarter last year.

Symbian also gave up market share, falling to 36.6 percent in the third quarter, down from 44.6 percent a year ago, while Microsoft Windows Mobile rounded out the top five with 2.8 percent compared to 7.9 percent a year ago. The momentum behind smartphones helped catapult Apple into fourth place overall in sales of mobile phones, ahead of RIM.

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