I think it really comes down to WP7 in competition with Android and Blackberry.
Apple's part in the competition boils down to people's choices of hardware.
It will be interesting to see how the market changes with iPhones on Verizon. Apple moved to VZW too late for me, though. I bought a ‘Droid late last year on a 2 year contract. I like it. Unless there’s some drastic change in the smartphone market, I’ll get another ‘Droid in 2012. My wife is probably going to ditch Blackberry for ‘Droid.