Stats are abundant, and everyone counts a little differently.  If you look hard enough, you can find stats to support any conclusion you want to draw.  One thing that is clear about 2011 is that there were definitely significant shifts among mobile platforms that played out differently across the globe.

Take a look at this graph, which shows that as an overall percentage on a global scale, SymbianOS still represents the majority of mobile web traffic.  This is driven by major mobile markets like India, Brazil, and others.  In this same context, Android has grown significantly, Blackberry has fallen, and while iOS lost some ground mid-year, its year-end market-share ended right about where it started off.

Zoom in on the U.S. over the same period, and a somewhat different story emerges.  Symbian has never been more than a blip on the radar, and Blackberry has walked off a cliff in 2011.  Android has grown most significantly, even overtaking iOS for a period before the release of iPhone 4S, which helped Apple finish the year with the highest activity market share.  Changes this year were so strong that the only two platforms that matter at the moment are iOS and Android.  Despite Windows Phone’s massive push last year, it still hardly registers at this point.

Jump oceans, and see yet another story across Europe.  Android is growing strong, and activity shares for BlackBerry, Symbian, and even iOS are the casualties.  Apple still holds a significant lead over Android, but if these trajectories continue, the two leaders could be neck and neck in just a few more months.

Zoom in on the UK market for another picture below.  BlackBerry is still strong, even above iOS for a period.  It has not yet seen the same drop-off in Britain as in other markets.  Android is growing, but has a long way to go, and Apple ends the year about where it started.

Further around the globe, check out Australia, where iOS continues to dominate by large margin, despite traction gained by Android.

These stats come from http://gs.statcounter.com.  As a bit of a data junkie myself, this site is a lot of fun.

UPDATE: A friend coincidentally posted an article today about how iOS is far ahead of any other mobile OS, based on data from NetMarketShare.  From looking at the data, I am pretty sure this graph is restricted to just the U.S. market.  These guys also count iPad as a mobile device, where StatCounter does not.  I tend to agree with StatCounter on this as studies have shown the iPad displaces significantly more desktop/laptop use than it does mobile phone use.  iPad’s share seems to make up the majority of the discrepancy.  It appears NetMarketShare uses a sample of about 160M hits per month, presumably on U.S. web sites, while StatCounter uses a sample of more than 15 Billion hits per month globally.  It is unclear whether either attaches the country attribute to the visitor or the site itself.  It goes to show that little variances in methodology can make an enormous difference in data, so ask a lot of questions when someone is using a pretty chart to convince you of something!