I have never done this but with an HMI.
If I was to try I would hook it up to a modem and play with it.
You can send ASCII codes to the modem "telling" it what to do.
Dial a number and also some ASCII text to show...
The overall price of this kind of work is more than the price for a small HMI that has this feature built into.
Install a second serial port on the Fx so you can monitor what is going on. It cheap...