For a more modern example of a bad choice of hold music, let’s take an example I have to endure on a regular basis, Month of Sundays by Passenger. At CD quality it’s got lots of interesting stuff going on, which you’d imagine might be ideal to distract someone from the fact they’re being kept on hold for ages. However, playing it over the phone it’s simply too busy. As soon as the brass and backing vocals kick in it just sounds yuck.
Don’t allow their holding time to be a waste of time for them or for you as a business.

For those still using analogue or digital phone systems, voice on ISDN circuits has a bandwidth of around 4000Hz. The audio from an analogue phone is sampled at 8000Hz, and because of the nyquist theorem, must be low-pass filtered to 4000Hz. So any frequencies in the audio beyond 4000Hz are lost. Interestingly, the human ear and mind are good at recognising human speech, so this is considered "toll-quality" voice, i.e. good enough to pay for. This is the reason why certain vocalised letters are difficult or impossible to tell apart on the phone. For example, the differences between B, P, T, C, etc. are almost entirely above 4000Hz.
If you would like a pause in your message where just background music (or blank airtime) plays, place (...) in your script where you want the pause.