A new image of an iPhone prototype has leaked out on the web. The image shows a very curved iPhone without a home button. Apple has also patented such design. See images in this vlog.
Personally I don't think Apple will release such iPhone this year, and when they do, it will not be called iPhone 5S because that will be designed as the iPhone 5 and only have some upgraded specs. Such new design like this will at least be called iPhone 6 or have a complete new name.
But it's interesting if Apple are experimenting with such device where the screen goes around the phone. If some one can succeed with that, It's Apple. They can make the user experience work for it. They are good at that.