The graph does not show it clearly yet, but looking closely at the end of the graph one can sense the end tipping upwards.
Since the beginning of April, with the release of the Nokia Lumia 900, the Windows Phone People Hub has been adding 100,000 Facebook users roughly every 2 weeks, rather than around every 3. This improved run rate has been maintained for the last month, with a hint of further acceleration, with the last 100,000 taking 13 days, and the one before 14.
Using our usual ratio, that gives us 13.65 million Windows Phone users, and suggests around 4 million Windows Phones will have been sold in Q2 2012, excluding any Chinese sales, which excludes Facebook integration in the People Hub. This would represent 200% growth year on year compared to the same period last year and 35% sequentially.
Hopefully we will continue to see an acceleration but current rates suggest 20 million Windows Phones for 2012 should certainly be possible.
Thanks jp for the tip.