I was going to buy an iPhone, but I went for a HTC HD2 in the end.
I agree with what was said above, the iPhone will always be popular, because it's "cool" to have one. There is millions and zillions of apps, which fart, let you imagine/pretend you're firing a shot gun, or swinging a light sabre. Anyone can pick it up, use it, and be happy.
The WM in general might take a lil more getting used to (if they aren't just using it straight foward), more of a techies phone. I'm guessing Andriod is the same.