Enthusiasts of the computer giant's products were able to see iOS7 which was unveiled by British design chief Sir Jonathan Ive at Apple's annual Worldwide Developers Conference in San Francisco earlier this year, with promises it would be an "important new direction" for the firm's software.
It puts more of the devices' features straight at the fingertips of users with a new control centre added which allows changes to key functions with a simple swipe of the screen.
The system has a "cleaner" look than its predecessors and has been described by Apple's CEO Tim Cook as "the biggest change to iOS since the introduction of the iPhone".
It was unveiled months after Apple posted its first profit slide in a decade and drew accusations that it has failed to innovate.
But its launch this week comes just days before two new iPhones go on sale - one of which features a fingerprint scanner.
Executive Phil Schiller sent a cheer through the audience at the San Francisco conference in June when he told developers that innovation remained key to Apple's philosophy. Industry observers appeared largely convinced and suggested the arrival of iOS 7 could go some way to silencing the critics.
The new software has been designed to make the iPhone appear bigger, with features crafted to take advantage of the entire screen.
Text is said to appear sharper, while a "control centre" on the phone allows users to adjust settings with one swipe from the bottom of the screen.
This gives instant access to functions such as Airplane Mode, Wi-Fi, Bluetooth or Do Not Disturb, and enables users to quickly pause or play a song, jump to the next track and stream music.
Meanwhile, a "notification centre" is available from the "lock" screen so users can view updates with a "simple swipe".
l BlackBerry is preparing to make deep cuts to its workforce by the end of the year. According to reports in the US, the move could lead to slashing the company's staff by up to 40%.