The first photographic evidence of that may have emerged in the form of two blurry pictures of what appears to be a very slim metal smartphone frame.
On the other hand it wouldn't be that surprising if they were legitimate. Apple has already slimmed down the iPad for the iPad Air, so it's not unreasonable to think that the Cupertino company might have similar plans for the next iPhone - maybe it'll even call it the iPhone Air.
The size seems about right too, as while it looks bigger than the 4-inch iPhone 5S, other recent reports suggest that Apple is working on 4.7-inch to 5.5-inch handsets.
That's all we have to go on so far, but if Apple really is working on bigger, slimmer handsets then that's a pretty huge change in itself. Anything else will just be the icing on the cake.
- We've reviewed the iPhone 6!