I would make those boxes as a TextViews (not EditText) - you don't want to have a soft keyboard opened and the user will be only using buttons below in order to enter verification code.
When the user presses number below - show it in the next available TextView, when every TextView is filled with number - verify whole code. The same should work backspace button - clearing previous filled TextView.
You might want to make TextView to be highlight when it is going to be filled with the next number press, you can do this with a state-list background.