Housekeeping is a mobile job. Room attendants move between floors, linen rooms and service lifts all day, and the supervisor needs to reach them without walking the building. The radio is the link between the floor and the desk.
The radio also has to be invisible. A loud alert in a guest corridor, or a housekeeper speaking into a speakerphone while a guest walks past, damages the guest experience. Earpieces, vibration and a clear floor-group plan solve most of it.