To change your voice mail greeting, pickup the handset, and dial 3566245, and when it asks for your pin, enter your voice mail pin followed by the # sign.
will put you at the voice mail main menu. To work with your greetings,
press 3. Next, press 2 to work with extended absence greeting. You
will press 1 to record the extended absence greeting. Follow the
prompts. Once you have the greeting recorded to your satisfaction, hit 3
Now, you will need to turn on the extended absence greeting. Hang up the phone, and dial 3566245 again and your pin again. Hit 3 to work with extended absence greeting. When she says "your extended absence greeting is turned off." Follow the prompts to turn it on.