iPhone OS 1 is the first major release of iOS. iPhone OS 1.1.5 is the latest and final version of iPhone OS 1. This version of iOS was the first iteration of Apple's touch-centric mobile operating system. No official name given on its initial release; Apple marketing literature simply stating the iPhone runs a version of Apple's desktop operating system, OS X. On March 6, 2008, with the release of the iPhone software development kit (iPhone SDK), Apple named it iPhone OS (they went on to rename it "iOS" on June 7, 2010). 
The update to iPhone OS 1.1.3 cost $19.95 for iPod touch users.