You might get better information using the WinSPM software to print a report, but from the screen shot it appears that the system knows that the slot is empty.
BACK UP THE SYSTEM TO THE PC CARD BEFORE YOU DO ANYTHING
Power down, move the VM card to slot 7, power up, do a Board Renumber, and test the Voicemail after the system restarts. If it seems OK, do another backup (don't overwrite the previous backup), power down, add the new 024 in slot 8, power up, Board Renumber, test it out. If you're still good with the voicemail running in slot 7, you're good to go.