OS X? Which Version?

It is anounced by Apple when the iPhone is released that iPhone is based on OS X system, which has been anounced as the most advanced operating system.
“This software completely redefines what you can do with a mobile phone”, said by Jobs.
iPhone is fully multi-tasking, based on OS X, so you can read a web page while downloading your email in the background. Apple isn’t saying, although when we asked a company executive if it was a weird, not-really-OS-X version of OS X, he replied: “This is OS X.”
To be more specific, it’s a version of OS X that’s been optimized for the iPhone hardware.
Apple’s statements lead us to believe that the iPhone runs a mostly recognizable version of OS X under the hood.