What buttons are required on android device? Typically there are three buttons on the device a back button home button and an overview button.

Which of these buttons are required by the standard or de facto standard?
There are 4 if you don't include Hardware Reset, three are mandatory: Home, Menu and Back.

See: https://stackoverflow.com/questions/3524758/are-the-4-android-buttons-standard-ex-back-button-menu-button - almost the same question, same answer.