Length – if your callers typically wait 2 minutes at a time, then at least 2 minutes of programming should be the goal. The idea is to ensure the callers don’t hear repeated messages every time they call. A typical on-hold message is 4-8 minutes in length.
The difference between writing a script and writing for print is that scripts must be written for the ear and written for effective delivery by voice talent. It must be written in a conversational tone. When you create a script that’s listenable, your callers will better understand your business.

Another great information you can put in your voicemail messages is to inform your prospects when you can reach out to them say the next morning or mid-afternoon and more so that they can be aware of when they can expect a call from you.
Voicemails don’t necessarily have to be monotonous or extremely jazzy or funky. What you’re looking for is a balance between the two. Whenever I call someone and their voicemail greeting is playing, it tells me a lot about who they are, as a person. Which is why, you’ve got to put a little bit of “you” when it comes to voicemail. And the best part about all of this is, since you couldn’t come to the phone, at least the callers are having a good time listening to the message.