You MUST use this adapter when connecting any of our phone recorders to a multi-line, PBX, or VOIP (Vonage) system. This adapter connects between the base of the phone and the handset or headset.
You do NOT need this on traditional, single-phone lines typically found in homes and apartments.
This handset/headset adapter will not work on cordless phones.
If you have any Internet-based telephone line, you need this adapter and a NON cordless phone. You will only be able to monitor the phone this adapter is attached to.