If I remember correctly, the iPhone he used with the screen sharing had wires hanging out of it... so you'll probably not want to go down that route...
If you are saying that there is a VNC server for the iPhone, that would address the lead question in this thread. Since I have looked hard for this and haven't found one yet, pointers in that direction would be appreciated.
On the other hand, if you are instead talking about a VNC client for the iPhone, yes, there are but this would not address the question that started this thread.
With a VNC client, you could use your iPhone or iPod touch to view/control other devices on which a VNC server is running such as a MacBook Pro.
With a VNC server on the iPhone or iPod touch, other machines with VNC clients could observe/control the iPhone.
"So rather than talk about this some more, let me show it to you. Alrightey. Now, I've got some special... special iPhones up here, they've got a little special board in 'em, and a... so I can get some digital video out, and I got a little cord here which goes up to these projectors, and uh, so I've got some great images, and you get to see what it really looks like." -- Steve Jobs @ MacWorld 2007, talking starting the demo of the iPhone.
If you can find some "special boards" and "little cords" to make yourself a "special iPhone", then sure