Buttons need some physical elements, cause if all depends of a large touch screen, a crack on glass and it's over.
Cell phone can't reach a space station without numerous antennas around the wold to help send and receive electromagnetic waves between cell phones and powerfull parabolic transmissor able to reach space, but Star Trek comunicators can.
Looking to original series props, I see no knov button, or no one that look like that.
