You could come up with the perfect business voicemail greeting, but if the quality is low, meaning there’s static, the volume is too low or too high, or words are getting broken up, you’re alienating your customers and allowing them to think they don’t care based off a very important first impression. And the solution is simple: call your number from your cell phone. How does your business voicemail greeting sound?
Domain = pepperdine (for non-students) Click on "Cisco Unity Assistant." On the main page, scroll down to the "Phone Password" fields. Enter a new 5-digit password in the "New Password" field; and re-enter it in the "Confirm New Password" field. Click the "Save" button at the bottom of the screen. Click the "Log Out" button on the upper right hand corner of the screen. Support

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.
You can also upload an unavailable greeting using the OnSIP app. After logging in, click on the Voicemail Settings gear icon at the far right. Make sure that the Custom Greeting is toggled to "on." You will then see an option to upload a .wav file of your choice. This recording will serve as your unavailable message.