Mashable notes this morning that the iPhone is no longer the most popular camera used by Flickr users. That honor now goes to the Canon 5D Mark II. Canon's numbers have been rising for months, and pics from that Canon model totaled 4,643 yesterday. The iPhone 4 users posted 4,460. The iPhone 4 was the number one image contributor when rankings were released last June.
There's one thing to take into consideration. The iPhone numbers only reflect the use of the Apple provided camera app. If you're using Instagram or Hipstamatic or any of the 3rd party HDR apps your photos won't be tagged as iPhone images.
Canon recently lowered the price of the 5D Mark II because its been replaced by the Mark III, so some of the boost comes from that. Also, numbers for the iPhone 4 are dropping as the iPhone 4S grows in popularity.
Looking at the trends the 4S may be on top soon, and as it is now, the iPhone holds the top 4 spots for camera phones on the Flickr tally. So there's that.