According to reports the iPhone runs a version of the company’s Mac OS X 10.5 “Leopard” operating system, slated to ship around the same time the iPhone hits stores.

According to Andy Ihnatko (Sun-Times):

“The iPhone runs the same OS as the Macintosh. … [I]t truly does run Leopard, the upcoming 10.5 OS that will be released for the Macintosh late in the spring.

Those spiffy UI animations, for instance, come courtesy of Leopard’s Core Animation suite.