[JnC]

What is unknown is whether or not the iPhone will "appear" like an iPod when docked. This might get a little tricky depending on it's file structure, but it's certainly possible.

If all the interface does is to pass audio, I think you're ok. If it passes control info like ff, rev, pause, etc., you're still probably ok. If it has navigation where it mirrors the filelist on the headunit, then you're beginning to get into uncertainty but still possible if the iPhone can "emulate" an iPod control interface.

I seriously doubt iPhone apps will be displayable on a iPod compatible headunit, as no knowledge about the iPhone was available when the headunit was designed.