iPhone is basically known for its UI (User-Interface) because its very attractive and outstanding too and accordin' to my information no company can beat iPhone in this matter but when we talk about features then really iPhone SUCKS because its a strategy of Apple not to allow all the applications at once so they are slowly making people fond of their iPhone...
On the other hand when we talk of Windows Mobiles they are way ahead of iPhone in respect to features and somehow also the camera but new IPhone 3G S has a 3.15 Megapixel Camera so its also in the competition...
If you are really willing to buy a mobile for features got for Windows Mobile and if for UI then obviously go for iPhone.
I see some people also talking of Nokia 5800 Xpress Music as a phone which can beat iPhone but really, no offence, just think what u're saying... Nokia 5800 is not even close to iPhone or any Windows Mobile because its a try from Nokia to bring a TOUCH SCREEN phone in the market as they wanted Nokia N97 to be successful but as results are in front of you Nokia 5800 started from a price of 60K but it is now at 25K so its a shame for Nokia.
Well HTC TOUCH HD and SAMSUNG OMNIA are two sets that have caused a great deal of trouble to iPhone...
Blackberry is basically a business phone and we are talking of MULTIMEDIA DEVICES so better keep it out of competition.
I hope my information will do you some good!!!