In the case of LACoFD they used the tones until they changed to a new computerized dispatch system.
Today all fire stations and vehicles have MDT's (computers) where they get their calls, send messages between vehicles, stations and dispatch.
When a call is dispatched the computer in the vehicles (and the station) beeps and a tone in the station goes off and the lights come on.
I believe they still have to old system in place as a backup should the current system fail.