If making the jump from the iPhone 4S to the iPhone 5S is daunting, or has already proved annoying, OptUX is the interface that would fix it. This allows one-handed use by intelligently recognising in which hand you’re holding the phone. But we say "would" as it’s just a design at this stage.
OptUX allows users the same interactivity as usual but with just one hand, even on the 4-inch iPhone 5S screen. Essentially it just uses the normal layout of iOS 7 but pulls everything to the side your hand is on for easier access. Whether that intelligently moves buttons to suit is unclear but you would presume that's the point.
READ: iPhone 5S review
This is just a design concept right now by Noel Joyce. But like all good ideas perhaps it will make it to the OS proper one day for everyone to enjoy.
It’s certainly a good idea and might make a difference in attracting new users who are afraid of large phones - or at least for current users to make the transition to a larger handset. Take note Mr Ives and don't be afraid to set foot in phablet city.