So far, Apple has released a major update to the iOS mobile operating system every time a new iPhone hits stores. Release dates so far have typically been seen every summer, with the exception of the iPhone 4S, released in October 2011.
iOS / iPhone OS Release Dates
(iPhone OS) iOS 1.0: Friday June 29, 2007
(iPhone OS) iOS 2.0: Friday July 11, 2008
(iPhone OS) iOS 3.0: Wednesday June 17, 2009
iOS 4.0: Monday June 21, 2010
iOS 5: Wednesday October 12, 2011
Apple's WWDC (Worldwide Developers Conference) took place in early June and Apple announced a list of new features coming to iOS 5.