In 2012, Android confirms its leadership in Mobile Operating Systems (Mobile in Focus #2)

As in many high-tech markets, network effects apply very clearly in mobile operating systems.  These effects usually result in a market tipping, that is to say, creating a competitive situation where winner takes all, leaving little space for strong contenders.
The winner before 2008 was clearly Nokia's Symbian, who was busy fending off upstart Apple, who took in 1 year a large chunk of its business.  2009 and 2010 were the years when Android spread like wildfire, reaching a share of 30-40% and becoming #1 mobile Operating System in terms of units.  It is important to mention this (market share of units), because performance differs greatly when we look at market share of sales and profits (refer to this article).  In 2011, Symbian bit the dust, BlackBerry and Windows ceded ground and the battle became a face-off between Apple iOS's integrated hardware and software platform versus Google Android's fragmented licensing approach.

For 2012 and later, estimates are a replay of 2011, with Android controlling over 50% of the shipments and iOS holding on to 25% approximately, and the rest far behind.  Android seems to want to replay the battle that Microsoft fought and won over Apple in the desktop PC market 25 years ago in this new smartphone market. In that case, Microsoft's licensing approach was best fit to a model of explosive growth channeled through OEMs like HP, Compaq, Dell, etc., while in this case, the specifics of the network effects seem to be a bit different.
In the PC market, Apple was unable to generate indirect effects for developers and retailers with a share which shrunk below 5% of the units.  With 25% of the units, in the market of smartphones, Apple seems to be in pretty good shape, generating a larger than proportional customer base (adding iPod and iPad users, and considering the iOS platform as one).  Also, in terms of developer preference (here) and third-party sales (here), Apple is the big winner in the market.  Therefore, it is able to maintain its position as a strong contender to Android, who is, by the way, suffering largely due to platform fragmentation, as seen here:

What is expected of the smartphone market? Analysts speculate that Android and iOS will coexist - maybe not so peacefully - while a new chapter of this fight is fought out in the tablet market ...