The ringing you hear is the beginning of the song that plays through the entire scene. The song is "Telephone Line" by ELO. Listen to it again, but this time, don't listen to Billy and Danny's conversation, you'll hear the song underneath their convo.
That's the intro to the song that plays throughout the scene, "Telephone Line" by Electric Light Orchestra. The beginning of that song uses telephone rings, which is why the guy in the song is singing, "Hello, how are you?" since he's making a phone call.