Contrary to this post over at Slashdot, "iPhone NOTE running OS X", John Gruber thinks that it really is and states his beliefs to why.
Gruber states:
"I’ve been investigating this since shortly after the keynote, and everything I’ve learned indicates that it is entirely fair and accurate for Apple to call the iPhone operating system “OS X”: the kernel is Mach;3 the low levels are Darwin; the UI for the apps is Cocoa’s AppKit."
He goes on to point out more things but we'll let you read this fine opinion piece on your own.
