The Viking E-20B telephone line powered entry phones designed to provide two-way handsfree communication. When the "Call" button is pressed, the E-20B will come off-hook and will remain off-hook until a CPC signal is detected, the programmed timeout has elapsed, a busy signal is detected, or the call goes silent, making the unit automatically disconnect. It can be connected directly to a C.O. line or analog PABx/KSU station when programmed as a ringdown circuit, or used with a Viking Dialer. If a line or station is not available, Viking's DLE-200B ring down circuit can be used.