Although previous rumors centered around slightly later release timings, like October or November, we're sure that everybody would just love if these September 21 theories come to fruition. This year, Apple is expected to launch a completely redesigned iPhone model, something which will probably set the standard for the industry for the next couple of years, at least in terms of overall design and construction.
On the software side of things, it's pretty much certain that the next iPhone will run on iOS 6, which was already revealed by Apple earlier this year. Although the new OS version will not bring a much-anticipated UI overhaul, it will still come with a bunch of cool new features, including improved Siri, Facebook integration, brand new Maps application with turn-by-turn directions, FaceTime over 3G/4G and so on. For a full list of new iOS 6 features, please see this post.
Thanks, anonymous tipster!