I have been searching for help on how to change my MAIN voicemail greeting for about 4 hours today.  I don't want anyone to EVER HAVE TO GO THROUGH what I did today.  So here is how you do it in a nut shell.

1. Dial FEATURE 983

2. password is 120000

3. click ok

4. Click AA

5. Press Grtg button

6. Press Grtg button again

7. choose which VM you would like to change 1 or 2

8. Press OK

9. Press Play if you would like to listen to the message you currently have recorded or

10. Press REC to change the greeting.

I wish you luck and Hope that this has helped!!