1. Press the voicemail button on your phone, or dial *97.
  2. Enter your voicemail PIN when prompted. The default PIN is 9999.
  3. Press option 5 for Advanced Options.
  4. Press Option 1 to record a new greeting, then 1 again for the first mailbox. Follow the prompts to complete the recording. Once it's done, the system will automatically set up the new greeting for you. 

NOTE: You can use *98 to access other mailboxes. *98 will prompt you for the mailbox number and voicemail PIN. Once you're in the mailbox, start at step 3 to record a new voicemail for that extension number.