Humor also leaves a lot of room for misinterpretation—which subsequently weakens sincerity and authority. A caller can be very turned off by merely misinterpreting your joke. Why take this risk? Additionally, this could even cause callers to question your character. Say, for example, the president of a company’s mobile phone voicemail greeting was funny. What’s to happen if the caller didn’t like or get the joke? What if they found it offensive? Another scenario is that a caller is reaching out to you for the first time—i.e. they have no idea regarding your personality. What next? The point is, with this type of greeting, humor is bound to be more divisive so just avoid it altogether. c. Poorly Pacing Your Message and Bad Time Management: Don’t speed through your message. Speak clearly so callers know what to include in their message and when to leave the message. At the same time, don’t drag your message out. No one wants to sit through a diatribe. Just get to the point clearly.
Scroll down to the “Greetings” section and click the speaker icon (manage) next to Voicemail Greeting. Click Add Greeting. Select the Record radio button. Enter the number or extension of the phone you wish to record the greeting on. Name the greeting. Click Call and follow the instructions given to you on the phone.

Website: https://www.snaprecordings.com/blog/the-top-8-voicemail-greetings-for-your-business
When leaving your voicemail and phone number, do not say, "Please call me back at ..." Nothing sounds more like a salesperson making a cold call then saying, "please call me back at...".