Under the advanced settings for the extension where is says Mailbox you’ll see 2001@device so you’ll just make it:
Now if 2001 (your extension) or whoever else you setup like that also have active VM you’re in the same spot. Your MWI light will tell you that the phone was told there is a new voicemail but you don’t know which one. Could be yours or one of the other two.
So keep in mind now as the user you’ll see your MWI light blink. Then you’re going to have to scroll to the “next page” on the phone to check the BLF for your two mailboxes to see which one is red/busy (meaning messages in the INBOX) and if those aren’t lit then they go “Oh it must be mine”.
The BLF buttons are the best option because they tell you which VM has a message instead of you fumbling around trying to figure out with of the three (or more) mailboxes actually have a voicemail.