The problem I guess is you just don't understand what all these professionals are explaining to you. Simple analog line is most fool proof. Not saying your wireless communication system doesn't have backups, but we are required to have something like 4hrs? of phone after loss of power. Old school lines used to power the whole kit and in catastrophic emergencies, say an earthquake, landlines are usually still functional. How's that wireless system going to hold up?

People have flat out died in elevators for lack of phone lines by owners, faulty dialers, etc. It is life safety for us, and therefor we prefer to Keep It Simple Stupid. Sorry that it may not save you a buck, but we as an industry believe it may save you a life.