The unavailable message is the standard greeting callers hear when they reach your voicemail box. It is the greeting that you can use consistently throughout the work year.
When you create a professional voicemail greeting, it can be a good idea to think about what your callers might want to know. After doing so, you can make a list of points to cover in your voice message; it might also be a good idea to write out the entire greeting on a piece of paper. The ideal message should be somewhere between 10 and 20 seconds, so you may want to time yourself repeating your message before you record it. After composing your telephone message, it can be a good idea to get a second opinion of this greeting so you can make sure it sounds professional. Writing down a voicemail greeting helps prevent mistakes when recording it.

It’s a good practice for each of your team members to have their own personal business phone numbers. There are many reasons why they shouldn’t use their personal cell phone number for business, so you’ll want to give them their own phone number through your VoIP provider or phone system.
For extension voicemail, extension users can choose how to play greetings in different presence: Default greeting: Play a greeting for any presence that doesn't have a personal greeting. Presence greetings: Play a personal greeting for each presence (available, away, do not disturb, lunch break, business trip, and off work).