You can assign different greeting sets to each voice mail port (the Primary Greeting set, Alternate Greeting sets 2 to 8, Alternate Greeting set 9 (if Voice Mail Hospitality/PMS is disabled) or one of the 30 RAD greeting sets).
To assign greetings to port:
Record the greeting via an administrators mailbox or upload the recording file via System Audio Files Update.
Assign names to the greetings (1 to 9) that you recorded in the previous step.
Assign the set to a voice mail port.