Sorry... I'm just not clear on what you want where....
Please recap the underlying problem, without too much about proposed solutions yet.
I "get" that there is a car with a driver.
The car is receiving messages by a telephone link, and you have a way to connect to the speaker of the "telephone"?
And you want to make a signal go from the car to a driver, who might be having coffee 100 m away from the car?
Where is the laptop? Is that in the car always, or does it go with the driver to the coffee place?
And where would the Arduino be? Does that stay in the car to handle the "come back to the car" message, or go with the driver to receive that message?
and in the car there is already mounted a auto-pager, (call system) with a usable input.
Is this the "telephone link" between the boss who wants to send the driver somewhere and the car? Or a way to connect the car to the driver in the coffee place? Did you mean INput, or OUTput? The "thing" on the autopager: Could you, say, connect it to a speaker to hear a noise, or is it more like something you would connect a microphone to, to feed someting IN to the auto-pager.... this is what I would call an input. If it is an input, what sort of thing would you connect, what would the arrival of something through the input cause to happen?