In selling 4 million units of the iPhone 4S in three days, Apple has hit the mark of roughly 16 iPhones sold per second, points out Shawn Blanc. The number is staggering when you consider that it is over double the number of iPhone 4’s sold on release day last year.

The availability of the iPhone on many more carriers this time around, including Verizon and Sprint in the US, likely contributed to its success. The initial reception by “experts” seemed to be fairly lukewarm as many appeared to be disappointed by the lack of a redesigned casing. This led a lot of people to claim that the iPhone 4S was doomed to be a middling release at best for Apple.

Shawn also makes an interesting observation that because the iPhone is selling so quickly, it is surely on track to bypass Microsoft’s Kinect peripheral for the Xbox 360 as the fastest selling consumer device of all time.

These numbers should all get a massive boost when the iPhone 4S becomes available in 22 more countries including Austria, Belgium, Czech Republic, Denmark, Estonia, Finland, Hungary, Ireland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Mexico, Netherlands, Norway, Singapore, Slovakia, Slovenia, Spain, Sweden and Switzerland on October 28th.