With the later models of iPhone it is no longer required to press the power button for some seconds to power ON the iPhone when it has been powered off. A very short button press will start the phone.
It is an inconvenience for me since I have one private and one company phone and there are occasions where I only want one of them on and the other off (mainly to preserve battery for later use) but the short press means that it easily powers ON while in a bag or pocket. Does anyone know if there is a (hidden?) setting to get the long press function back?