The announcement that Microsoft is acquiring Nokia's handset business is a recognition that Windows Phone and Nokia devices are attached at the hip and are in fact one business not two. It is also apparently a recognition that Nokia was running out of cash and needed to do something big.
So now we have three fully integrated mobile OS and handset companies (Apple, Microsoft, Blackberry) and one fully integrated mobile OS and handset company with an OEM ecosystem that is sort of working (Google). Android is open source so we are likely to see it in various flavors (Amazon Android, China Android, etc) for a long time to come. It is also possible that Samsung and others figure out how to fork Android into something they can control and own.
My view is twofold. One, that Microsoft had to do this. The future is in mobile devices not PCs and they need to increase their focus and investment on Mobile. I am not sure this will work, but I also don't see that they had a choice. Two, that this changes nothing. Android and iOS are dominant and becoming ever more so.
My bet is two plus two equals two, not four.
For more excellent analysis, I give you Ben and Ben:
