An advanced mobile operating system is within the the IPhone 4.
iOS 4 is the fourth major release of the iOS mobile operating system designed by Apple Inc. , being the successor to iPhone OS 3 .. iOS. iOS. iPhone OS 3. iPhone OS 3. fourth. iOS version history. mobile operating system. mobile operating system. It was released on June 21 , 2010 , and was the first major release to be renamed to simply `` iOS '' , and the first major release to drop support for some devices , as well as the first update that iPod Touch users did not have to pay for .. iOS. iOS. iOS 4 was succeeded by iOS 5 , which was released on October 12 , 2011 .. iOS. iOS. iOS 5. iOS 5