You don’t have to spell out every single thing that you think they might want to know. Have some faith that your callers will be able to figure things out on their own. Be natural but informative.
Typically, most of these services are uniform—i.e. include the same tools and features (send a script, they record it in a tone you approve, they send it as a file, you supply any feedback, etc.); however, there are some services that go above and beyond. For example, VoiceOverPro, is a single voice professional who records 30 second voicemail messages based on users’ scripts. This is standard; however, users also have options like adding music, recording up to 60 seconds (or 150 words), rush, 2-day turnaround, and even same day delivery.

There are three parts to a perfect on hold message: the script, the speaking tone and the written tone. And of course, there is also the music, which plays a big part in representing your business brand.
Simply speak into your phone or computer while recording a greeting with your business phone service. If you need to create your own audio file, the voice memo app on your phone should do fine.