The Samsung Galaxy SIII has been this years bestselling Android phone and now it even surpassed Apple's iPhone 4S. This is a huge feat for a single Android device. While as a whole, Android phones ship more units than the iPhone, the fact that a single Android device did it is quite an accomplishment from Samsung.
In Q3 the SIII sold 18 million units, while the iPhone 4S shipped 16.2 million devices. There may be an explanation for this. The fact that the iPhone 5 was on the horizon probably slowed 4S sales, but that really doesn't lessen a growing trend.
I think that Android as an OS has grown into a smoother, less buggy experience. And for consumers stuck with a 3.5 or 4 inch iPhone, they see these new Android devices with large screens, less lag, and more features and they are starting to shift to this platform.
I know what your thinking, once we get the iPhone 5 figures we will likely see record sales. The iPhone 5 will probably outsell the Galaxy SIII in Q4. But to me it doesn't matter, the Galaxy SIII came out during the summer and the iPhone 5 came out in September. So of course the iPhone 5 will sell better in Q4. But I think we will continue to see consumers slowly move toward Android and other alternatives.
It will be interesting to see where Android and iOS will go in the future. Will Microsoft be able to break in, is Blackberry 10 dead in the water? The next few years will be interesting indeed.