The classic phrase "historical trends are not an indicator of future performance, shares can go up as well as down" applies just as much to analysts' forward-looking statements in company reports as it does to predicting how many phones, that we have no idea about (because they've not been announced yet), will sell. It's possible that any one of the current mobile operating systems could suddenly spike in sales - after all, a single appearance on the Oprah Winfrey show was enough for many book authors to become best-sellers... or fall off a cliff, perhaps due to a patent lawsuit stopping the sales of a complete portfolio.
We don't know what handsets are planned by the manufacturers, and you can be sure that a lot of innovation is going to be added to the standard "touch screen slab" that many people now expect in a smartphone. Specifications can always be improved, and camera technology is still seen as a key consideration in a purchase.
ZTE and the low cost manufacturers have a disproportionate part to play as well in the market share - the high end handsets might get the reviews and the awards, but the low end is where the bulk of the numbers will be sold. Where their loyalties lie in 2012 may also have an impact.
What about areas such as NFC technology, LTE networks, mobile payments, new battery technology, or something as humble as external microphone sockets? Image the impact of a killer piece of software that comes out locked to a single platform - what would happen to Windows Phone if a mobile version of Halo appeared that knocks the socks off hardcore gamers?
Not even a Univac can help predict the future (Trey Ratcliff, Flickr CC).
All these ideas, all these potential modifiers, yet people can still come up with a concrete percentage? Naturally, it's what humans do....
So let's try a little experiment. What do you think the market share of Windows Phone will be at the end of 2012? Give us your percentage, and whatever factors will have the most impact on the final number. No prizes, but I think we'll all be intrigued to see what everyone is looking at.