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For the OP, I would disconnect the push button and wire it to an actual doorbell.

Some doorphone versions had another set of dry contacts on the push button that were brought out to the terminal block for exactly that purpose. You could use those for the door bell and connect the T&R to a regular analog extension. That way someone could pick up a phone and talk to the visitor if they wanted to. If nobody picks up the extension it should time out.

But the big question is what doorphone does he have.

-Hal

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