i see it much like the PC OS market, there's no (real) OS that rules them all, i think windows has the leading share, but it's not really a monopoly, linux and OSx both have reasonably high market shares.

in a way it's sort of like the PC market, except i would expect the order goes: ios » android (linux) » windows mobile, i have no idea where symbian would be, but really don't care, or the generic dumb phone os's, I'm just looking at the main 3