The American’s with Disabilities Act (ADA) specifies many applications that need some form of communication whether it be two-way voice communication or some form of visual indicator. When a telephone or intercom system is required, then the ADA has defined height requirements so people in wheel chairs can easily access the controls.
When a communication system is required, one of the main ADA requirements is how it is positioned regarding its height. The highest operable part should be located no higher than 48-54 inches above the floor depending on whether the installation location requires forward reach or allows for side reach as seen in the illustrations below. Also, objects projecting from walls with their leading edges between 27 in and 80 in above the finished floor should not protrude more than 4 in into walks, halls, corridors, passageways, or aisles.
The ADA requirements are detailed here: ADA Installation Requirements Illustrations
More info about ADA compliance can be found here: Use Wireless Callboxes for ADA Compliance