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.
Phones are assigned to people or to office names. For example a phone could show “MAU Plaza” or it could show a user’s name. If the phone is assigned to you, it will have your UNI email address associated with it. There are various kinds of voicemail greeting options in the new UNI Voicemail system. When you initialize your voicemail box for the first time, the system has you set up two of your default greetings, which consists of your (external) personalized greeting and your name greeting. You can access your greetings via phone or via the UNI voicemail web portal.

You can’t just make any voicemail message and think that it’s going to be the right fit, your voicemail messages need to have the following tips below so that it can function as a lead capture when you’re not present.
"You see a lot more people working on collaboration technologies where you can share and exchange information in more social media-like contexts," he says.