Apple has announced that the iPhone 4S (which saw a million pre-orders within a day of its announcement) has sold 4 million units in its first three days on the market. The sale rate is more than double the iPhone 4 and is the fastest-selling phone in history.

“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 Apple senior VP of Worldwide Product Marketing Philip Schiller. “iPhone 4S is a hit with customers around the world, and together with iOS 5 and iCloud, is the best iPhone ever.”

Additionally, over 25 million customers have also downloaded the new iOS 5 operating system for their iOS devices.