Your phone system can be a powerful marketing tool for your business, and that includes your voicemail greeting. If you want to utilize this opportunity to throw in a quick humblebrag and keep callers informed of your awards and accolades, there are a few best practices, you should follow. First, keep the self-promotion brief and appropriately placed within your voicemail message. Don’t promote yourself and your products/services in the same greeting, and finally, only include current achievements in your business voicemail greeting.
You might also consider giving them the option to skip your voicemail message completely by pressing another key (again, check with IT). You also want to make callers aware what you will return their call, instead of telling them that you will try to return their call--and let them know when you are likely to do it, if possible. If necessary, provide additional or emergency information in your voicemail greetings. My dentist, for example, lists his cell phone number for emergencies.

Hello, you have reached the dental office of Dr. X. We are busy assisting a patient now, but will call you back as soon as possible. Please leave your name, reason for calling, and your number. If this is an urgent enquiry, please call 911. In this case, the dentist is giving a reason for not being available and they’re providing a way to prioritize the patients who need the most help. They’re also leaving an emergency number for the most severe of situations.
Your prospects are under the impression that a brand will be always available to cater to them, now for some circumstances, a few brands might not be able to serve their prospects 24/7 which is why creating a voicemail message becomes useful.