Whether it’s an out-of-stock product, a canceled event, or social media snafu, there are times when your business may see an influx of frustrated callers. While it is important to address their concerns head-on, you may not be able to answer each call as it’s received. Make sure you use best practices for dealing with angry customers, and that your voicemail greeting sets the appropriate tone. Avoid defensive language, validate their concerns, and keep them informed as to how you are handling the situation.
The phone you use to record your greeting – and your surrounding – can turn your carefully scripted greeting into an unprofessional mess. Background noise is terribly distracting, so choose a quiet room or parked car to make your call. Landlines, or a “wi-fi enabled” cellphone call, can provide much better connection quality than a standard cellphone. If you must use a cell phone, be sure to use a high-quality headset for the best clarity.

Website: https://techcommunity.microsoft.com/t5/skype-for-business-blog/skype-academy-voicemail-transcript/ba-p/58816
Telling a quick joke or including a little more information can keep you safely within the 20-second timeframe while letting the caller understand a little more about you.