Specific FeaturesBase Model* | CE20 Line Powered Ringer / Backplate | Ring Detect Relay (RDR)* | Ring Detect Relay (RDR) / CE20 Line Powered Ringer / Backplate | Ring Detect Relay / Headset | Headset (in lieu of Handset) | Ring Detect Relay (RDR) | Headset / CE20 Line Powered Ringer / Backplate