How popular is the iPhone one might ask? Well the iPhone (at least up until the 3Gs) has had a fairly cruddy camera. It does ok, but even now, no flash, low megapixels, which to be fair, compares to other phones, but still, not great.
Check out the Flickr charts on camera usage. The first one is all cameras, then the third chart are phone cameras.
That will tell you how popular the iPhone really is: