Aside from a few apps (most of which aren't really doing anything on the iPhone that would make them impossible to implement on a different platform if the developer felt it would be worth porting it over to say Android or WebOS), the only thing I really need for an "iPhone-killer" to have is the ability to sync with my Address Book and iCal on my Mac. Perhaps I'm missing something, but that seems like something not available on anything other than the iPhone (I'm fully prepared to be told I'm an idiot for not realizing other phones can do this too, though
).