7 major versions · counted separately from hardware
This entry separates the first iPhone software from the device. It uses "iPhone OS 1" as a retrospective catalogue label, not a proven 2007 trade name: Apple's archived page calls it OS X. The iPhone announcement was January 9; Apple set the US sale for June 29, 2007.
Apple presented the iPhone 2.0 beta on March 6, 2008, with an SDK and enterprise features. The initial June forecast is not the final date: the July 10 release announces the iPhone update for July 11. Beta and final release are separate milestones.
Apple previewed the iPhone OS 3.0 beta on March 17, 2009. Its June 8 release set the general update for June 17; AppleInsider's original report that day documents the rollout. Beta, announced date and observed availability are separate milestones.
Apple previewed the beta as iPhone OS 4 on April 8, 2010; by the June 7 iPhone 4 announcement it called the system iOS 4. These are names for the same major version, not two separate systems. Apple announced the free update for June 21 through iTunes 9.2 or later.
Apple previewed iOS 5 on June 6, 2011 and announced the free update for October 12 through iTunes 10.5. iPhone 4S was introduced with this system and an announced October 14 sale in the first markets. Apple's October 17 report already records iOS 5 users after release.
Apple previewed the iOS 6 beta on June 11, 2012 and announced the free update for September 19. iPhone 5 was introduced with this system. An Apple release dated September 24 confirms that devices had already been updated; the announcement date is not treated as proof of actual availability.
Apple unveiled iOS 7 on June 10, 2013 and announced the free update for September 18. It changed the interface with revised typography, translucency, layers and motion. iPhone 5s and iPhone 5c were announced with this system; Apple's September 23 report confirms its use after launch.