Apple just announced that the iPhone 4S topped 4 million in sales for its first weekend of availability.

On top of that, over 25 million customers are already using iOS 5 in the first five days of its release. Over 20 million customers have signed up for iCloud.

“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 SVP 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.”

The new camera and Siri have been big draws for consumers in purchasing the iPhone 4S. It’s hard to deny that Siri is just fun to mess with. I see the appeal. Case in point: iPhone 4S’ Siri: Now with More Easter Eggs.

Of course the 4S is the first iPhone available for Sprint customers. That has to be huge on its own in terms of boosting sale. The addition of Verizon to the iPhone availability roster was certainly helpful when that first happened.

The iPhone 4S is currently available in the US, Australia, Canada, France, Germany, Japan and the UK. It will be available in 22 more countries on October 28, and in over 70 countries by the end of the year, the company says.

View more iPhone 4S coverage here.