does anyone know what the things are that store use to play music then when they pick up the intercom and the music dies off and when they put it down the music come back on
It doesn't have a specific name it's a feature of some intercom systems. Basically there's a circuit that detects when the intercom is in use and mutes the audio.
Most stores or businesses use either a multidisc CD player connected to a PA system or they subscribe to satellite music service also piped through a sound system.
does anyone know what the things are that store use to play music then when they pick up the intercom and the music dies off and when they put it down the music come back on
The function is sometimes called an audio 'ducking' circuit. That's where the microphone audio is detected, and automatically 'ducks' the music to a predetermined lower level. (not usually completely off).
The circuit is usually part of the public address amplifier. Similar circuits are used by radio broadcasters and DJs. Again the function is usually built in to the mixing equipment.