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.
The decision to update your on-hold message depends largely on the content you are sharing. If you are sharing content that includes short-term promotions, this information will need frequent updating so consumers are always aware of the status of any offers. However, if you’re only sharing general information about your standard products, your operating hours and location, then the decision to update the message can be more reliant on metrics.

You will most likely run into the typical Stalingrad-esque repeating messages that state how important your call is to the business. It is only slightly less annoying to have some form of default music that plays on a loop, and gives you the virtual experience of being stuck in an elevator, listening to muzak ad infinitum.
Hold music is also not supported in consultative transfer of a PSTN call. Call answer/initiate (by name and number) Lets users answer inbound calls with a touch, and place outbound calls either by dialing the full phone number or by clicking a name in the client.