See if we can revive this question. On our campus, we are seeing requests for pass-thru windows with speak thru voice openings and pass-throughs as a response to COVID. I think the pass-thru can be reasonably addressed by 904 but I don't find anything about the height of speak thru holes in glazing. Seems appropriate to me that a voice hole should have a hi/lo configuration.
904.3.1 Vertical barriers. At service windows or service counters, any vertical barrier between service personnel and customers shall be at a height of 43 inches (1090 mm) maximum above the floor. Exception: Transparent security glazing shall be permitted above the 43 inches (1090 mm) maximum height.
904.6 Security glazing. Where counters or teller windows have security glazing to separate personnel from the public, a method to facilitate voice communication shall be provided.