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.
From young, professional US – Neutral voices to Australian, Spanish, and UK voices.

11 On Hold Message Script Ideas. The main focus of your on hold messaging is to relay information that would be helpful to people wishing to use your services, buy your products or visit your shop, store or showroom. Feel free to use the template messages for your on hold messages or just to get ideas. Just replace [the words in brackets] with
We offer affordable rates. That way, you can take care of your clients and get set up with a custom phone message that doesn’t break the bank! Our goal is to ensure that your clients’ time on hold is being used to your advantage. That’s why we make sure that creating a custom hold message is affordable and fits your budget. Simply get in touch with us and we’ll help you find the best on hold message or music that still works for your company’s monetary needs.