I think we all knew that the iPhone 4S was going to be a seriously popular device when it finally launched after all of the rumors and frenzy surround the device leading up to that launch day. Flickr has a camera finder page that keeps track of the most popular cameras used on the service are. It's no surprise that before the iPhone 4S launched, the iPhone 4 was the most popular camera.
The iPhone 4 is still at the top of the list, but before the 4S camera around the iPhone 3G was the second most popular camera. Shortly after the launch of the iPhone 4S, the 3G dropped quickly and the iPhone 4S camera took the second most popular spot.
It's interesting that out of the top five cameras on the service, four of them are the iPhone. The only non-iPhone on the list is the HTC Evo 4G in last place. The iPhone 3GS is the fourth place device, the iPhone 3G is third, with the 4S in second and the iPhone 4 in first. The 4S is a long way from the iPhone 4 in popularity though.