Like a time travel scenario where you meet your own grandfather as a child, enthusiasts working with the Einstein Newton Emulator project have ported the Prodigal PDA to the iPhone. The current implementation is only available as source code and runs a bit slow, but is an actual working version of NewtonOS complete with handwriting recognition and familiar input gestures.
Apparently a submission to the App Store is planned, but chances of approval seem slim since as Apple never looks backward; ultimately this hack may require a jailbreak to run. Regardless, emulators are a wonderful way to keep old technology alive, and the Newton was a groundbreaking device on many levels.
The circle is now complete. Obi Wan would be proud..