Our code here is that it has to be a dedicated POTS line and it is tested and documented on the elevator inspections.
Most elevators come with everything installed already (phone and auto dialer), just needs the line run to it and programmed.
Another code/restriction here is that we are not allowed to run that wire in the elevator mechanical room, it has to be done by licensed elevator technicians. Most of the time, they allow us to do it and just stand and watch.
