The first generation i Pod Touch and i Phone have i Phone OS 3.1.3 as their newest available version. On June 21, 2010, i OS 4.0 (formerly i Phone OS) was released to the public and was made available only to the i Pod Touch and i Phone.
i OS 4.0 was announced to have over 1500 new APIs for developers, and included the highly anticipated multitasking feature.
The final 1.x series release was 1.1.5, released shortly after i Phone OS 2.0.
July 11, 2008 saw the public release of i Phone OS 2.0, with upgrades through version 2.2.1 made available.
i Phone OS 1.2, which after the first beta was replaced by a 2.0 version number; the second beta was named 2.0 beta 2 instead of 1.2 beta 2.