Just as you could run Windows Mobile apps on the N900 - if someone spent 10 years working on an API compatibility layer.

Granted, the iPhone should be simpler as a lot of the core OS is the same and many bits which the iPhone relies on are open source. However it would still likely take years of hard work to fully emulate and by then Apple will have changed so much.

People need to remember, just because something CAN be done, doesn't mean it can be done in a time frame that is useful. It also doesn't mean they wouldn't get sued to death long before it reached usability status. It doesn't even matter if it was proved to be legal, you would need the money for court costs to fight it and it would take money/time away from the project itself.