Otis Elevator has been out of business for many years.
If you want to be safe just provide a dedicated POTS line.
Every locality has an elevator code and the larger municipalities will have their own elevator inspectors. Contact the building department for information. They will point you in the right direction.
Not knowing where the phone is supposed to call is a common problem and not even the elevator techs on a new installation will know the answer because they are all over. Whoever is in charge of elevator inspections will have the answer.
-Hal
