Apple on Monday said  that it has sold over four million of its new iPhone 4S, just three days after its launch on October 14.

It said that more than 25 million customers are already using iOS 5, the world’s most advanced mobile operating system and the device is available in the US, Australia, Canada, France, Germany, Japan and the UK, and will be available in 22 more countries on October 28 and more than 70 countries by the end of the year.

“iPhone 4S is off to a great start with more than four million sold in its first weekend—the most ever for a phone and more than double the iPhone 4 launch during its first three days,” said Philip Schiller, Apple’s senior vice president of Worldwide Product Marketing. “iPhone 4S is a hit with customers around the world, and together with iOS 5 and iCloud, is the best iPhone ever.”