The HC-1 connects in series with the handset of any telephone using modular connectors. Since a connection to the telephone line is not required, the HC-1 can be used with almost any telephone in single or multi-line, modern electronic or older key systems. Pressing the front panel button disconnects the handset and connects the external audio in/out jacks to the telephone. Releasing the button reconnects the handset, allowing normal use of the phone. External audio is connected via separate input and output jacks. Both inputs and outputs are 1/4 TRS jacks wired so that you may use either balanced or unbalanced connectors. Please note: This is not a telephone hybrid. It is not suitable for conversing with telephone callers on-air. Model Excalibur HC-1 Handi-Coupler.