In December, the iPhone managed to push its way into the top 5 Flickr cameras, overall. Now it seems the device has managed to push its way past the Canon Eos Rebel XTi, according to Flickr's Camera Finder
However, it doesn't appear that it maintained that lead. Since the LA Times wrote
about it, a newer graph seems to show that the iPhone and the Canon Eos Rebel XTi are neck and neck again.
I wouldn't put any stock in this being something intentionally done by Flickr to satisfy the (as the LA Times puts it) "elitist photographers" at the site. More likely it's simply because the Camera Finder updates all the time.
#1 or #2, it's still impressive. Among camera phones, the iPhone has long held a huge lead in that category. Since the iPhone is one device that's gotten users to start using their phones for the Web, and not just for calls, it's obvious that users are more likely to upload their photos than say, a Windows Mobile user might be.