Theres simply zero competition when it comes to VNC on iphone (and to some extend, other handsets) vs n900. Here's why:

Resolution: on IPhone you are forever pinching pinching pinching.. to zoom. The IPhone tries to be smart to recognize a pinch or a swipe not as a click through to the VNC server. N900 with 800x480 involves a lot less scrolling, and does away entirely with zoom. If you touch the screen, the click instantly goes through to the vnc server, as you would expect.

Right and middle click: on n900, hold "plus zoom key" on the top of the device then click the screen for a right-click, or hold "minus zoom key" for middle mouse click. Fast and usable. On the IPhone.. ?? i still haven't worked out how to right-click. I'm sure there's a way, but with no hardware buttons to act as a right-click modifier, its sure to be annoying.

Hardware keyboard. Type away on the keyboard of the n900, and you can still see all 800x480 pixels of whats going on, in the VNC session. This just aint possible on an IPhone.

Multitasking: want to switch between browser, IM chats and VNC sessions? (a very common scenario for someone using a VNC client). Want to have multiple VNC sessions to different PCs? not possible (or very difficult) on IPhone.

Ive used an IPhone for a while as a VNC client. When you need to VNC into something, after a while you subconsciously start looking around for a spare PC with mouse and keyboard. There's the feeling of "i could use my IPhone, to VNC into the remote computer, but its just too frustrating.." There is no such feeling with the N900. You log in, quickly perform the required task, and disconnect within seconds.

There's no way someone could claim that VNC on IPhone presents any competition here. Did i mention you can VNC into your N900 from a PC? (see x11vnc app)