This is going to take some getting used to...hopefully I don't say something I don't want the person on the other end to hear. I've always hung up a call on my iPhone by pressing the power button, just second nature. And it used to work whether the phone was up to your face or not (with the screen off) but it seems Apple has disabled that? Maybe in an attempt to prevent people from accidentally hanging up with the button now on the side? Now you have to move the phone away from your ear (so the screen lights up) before you can use the power button to end the call it seems.