Where is your evidence supporting the claim that Apple owns 50% of the market? That is way above the figures I have seen. Seems to me you are just pulling metrics out of thin air in this post.
I focus on the US (and UK and Japan), it's a two horse race. You can segment it all sorts of ways. iOS is somewhere between 40-60% in a given segment, and usually around 43-48% overall. Overall share has been declining as the market growth slows and prepaid plans make total device cost more relevant.
Nothing I said means anything ex US, as the solutions, costs and requirements vary.
