... support 3 ways for recording:Voltage Control: record according to the change of the voltage, that means start to ... record when you answer, stop when you hang off.Audio Control: record ... audio signals, likes intercom, sound pick-up.Key Control: control the record by key, you can start or ... 823,G.737,G.739,G.742-1988Phone Mode Voltage Standard:70-100V(Ring) 20-48V(Idle) ...