Talk-Back paging is still interfaced through a trunk port (although you could use a Tip/Ring station port and a "Centrex" paging adapter). The amplifier or a zone page adapter will have the talk-back capability in it, and you are limited to the number of speakers in a talk-back zone, usually 2 max.
I've never been particularily impressed with talk-back systems, but if the location is not expecially noisy, you might get away with it.