2 Button. The Videx 3171A is a full base digital audio phone suitable for use with the VX2200 digital audio and video systems. It has an electronic call tone, adjustable 3 level volume control, a door open push button and a spare service button. . Electronic 2 buttons. 2 wire BUS digital audiophone. Call tone adjustment switch: 3 level (low, medium and high). Number of rings adjustment: 2 way internal jumper (3 or 6 rings)