According to ComScore, Android is now (back) at 51% market share. It actually achieved this market share earlier last year, and has mostly stagnated around 50%, but then the big iPhone 4S launch came, and dropped Android's market share for about a quarter by a few percentage points. But now Android is back at over 50%, and iPhone's market share increased as well by 1%, taken at the expense of RIM and Microsoft.
Speaking of Microsoft, these numbers actually show installed base for the new quarter, not the new sales done last quarter, so the 3.9% number actually refers to the installed base of both Windows Mobile 6 users and Windows Phone 7 users. But this also means that WP7 is not growing fast enough for the total user base to increase in market share. It means Microsoft is losing users faster than they are making them.
RIM lost quite a bit last quarter, and if this keeps up, even Blackberry 10 might not save them this fall, but as I said before, it all depends on how well they execute the launch of BB10. If the BB10 OS and its ecosystem is half-baked at launch, then the downwards trend will continue for RIM, and probably nothing but an acquisition would save them. I'd strongly suggest them they try to license the OS to as many other manufacturers as possible if they want it to mean anything. At the very least it could become the 3rd ecosystem behind Android and iOS.
Right now Android is still looking strong, although in US it seems to have stabilized, and will probably remain at 50%, not a bad market share at all, while globally, they will probably surpass 60% and maybe even 70% thanks to poorer countries like China and India, where they obviously can't all afford iPhones.