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.
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.

We strongly recommend that you write short, independent messages, with a musical interludes. The volume of the music should be turned down during narrative messages.
Check out our on hold players as we are offering great deals when purchasing the on hold player and message as a package. As a business you aim to keep your clients on hold as short a time as possible, sometimes this can't be avoided. You want to take