What can it do that the N800 cannot? It can sync with PIM applications. That's a biggie.

Other than that, there isn't anything major that I can think of that the iPhone does that the N800 does. HOWEVER, the appeal of the iPhone doesn't necessarily lie in the fact that it can do absolutely everything, but that it does a lot of very important things very well and in a very slick and easy to use interface.

For example, the web browser is infinitely more usable than the N800 browser. It's slicker, more responsible, easier to navigate. The text input is considerably better than the N800. The navigation around the iPhone is very slick, very easy to use and very well designed.

The iPhone is an example of what Apple does best. It develops a functional product that has a user interface design par excellence.