Do you know why the Enter button is the biggest button on the keyboard? It is because it is the most important button. The Enter button does one of two things. When you hit the Enter button, it is an act of launching an action while you wait for the result. Or, it is a full stop for you to pause before taking the next set of actions.
I wish every smart phone has such a button. When I use it to take a picture, touching the screen to get a shot is a far cry from the snap action that comes from pressing a shutter release. When you press a physical button - the "Enter" button - you execute a decisive action.
When making a phone call, I prefer to press a physical button than to touch the screen, after entering the numbers. It feels more responsive. Press a button, then wait for the call to go through. That's execution. The same with using a calculator app. After you enter the numbers and the operators (+ - * /), you hit the Enter button to get the result. When I use a recording app, I want an Enter button to start and stop recording. When I use a music player app, I want an Enter button to start /stop the music. We are all trained to press Enter at the end of every set of actions.
You cannot replace the Enter button with a touch screen virtual button. It just doesn't feel the same. So why is there no equivalent of an Enter button on every smart phone? Wake up, Apple, Samsung, and HTC! (hit Enter)