I think you have to have a CallerID support modem. The modem gets the number of the caller, if your telephone company supports that feature and enabled you to use it. That's how it knows who calls. It has nothing to do with the Alarm panel.
I'm not sure that I'm right here but I don't think there's any other way to get the caller number.
I don't think my modem supports CallerID

But I still like the idea of this panel.