Which killer features?
For what do you need multitasking on a phone? How would multitasking be different from how iPhone does things (you switch between apps)? Only use I could think of it is audio-streaming or something like that. Multitasking might make sense on normal computers, where you can have several app-windows open, and you could move stuff between them. But that is not possible on a phone. Phones display one app at a time.
Hell, you don't really multitask on a computer either. Or do you edit spreadsheet and presentations at the same time? No you do not. You do your tasks one at a time, switching between different apps. And you can do that just fine on the iPhone as well.
One thing I can think of which would be extremely useful would be an IM client.
I can give examples until I'm blue in the face and some people still wont be convinced.
If you dig for shit in any system, even one you'd think was perfect, you'll find it.
Bus error -- please leave by the rear door.
