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Apple have announced that over 4 million iPhone 4S's were sold in the smartphone's opening weekend, more than double the amount of iPhone 4's sold over the same period last year.

The company also said that 35 million customers have dowloaded iOS 5, Apple's new operating system, since its launch on October 12, despite thousands of users experiencing major problems with the upgrade.

Philip Schiller, Apple's senior vice president of Worldwide Product Marketing, said in a statement: "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.

"iPhone 4S is a hit with customers around the world, and together with iOS 5 and iCloud, is the best iPhone ever."

Over 20 million customers have subscribed to iCloud, Apple's cloud-based storage service.

The iPhone launced in the US, Australia, Canada, France, Germany, Japan and the UK on October 14, and comes to 22 more countries on October 28.

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