You can change your voicemail greeting at any time. For example, if you're going to be out of the office, you can say so in your personal greeting. You can inform callers about the reason for your absence and tell them that you'll return their call later.

1. Press Messages 
2. Enter your PIN (Default is 12345)
3. Press 4 to access Setup options.
4. Press 1 to listen to your current greeting.
5. Press 2 to record a new greeting, and press # when you finish recording.
6. If you are happy with your new greeting, press 1 to save it, and press * twice to exit.