The most common use of background music is to play something while the caller is waiting for something to happen. Playing background music during prompts is not recommended.
The background music is effectively mixed in with the prompts: the caller should be able to hear both if both are playing at once. Figure 1 shows what the caller is hearing at each stage in the interaction, on the telephony channel and on the music channel. If required, you can turn down the music during prompts.