I bought this so I don't have to unplug and plug it back in https://www.amazon.com/Sentry-Industries-Inc-CT-CID868-Blocker/dp/ B019ERMS90/ whenever he set the state of the phone to "Line Busy". After connecting it between the cable connected to the line port and the Sentry call blocker, the line will no longer randomly be used after the call ends. The only issue I had was that there is a hiss before the dial tone letting you know it's ready to ring (perhaps buying another one and plugging it into a phone cord would fix that). I recommend it for use with the product mentioned, as well as for DSL modems etc.
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