A voice mailbox management method in a voice mail system through a mutual notification function, between a user mobile telecommunications terminal and a voice mail server, using an extended short message service is provided. According to the voice mailbox management method, when a state change occurs in the voice mailbox of the voice mail server and the voice mailbox of the user mobile telecommunications terminal, a short message indicating the state change is sent to each other, and according to the received short message, the state of the voice mailbox in the voice mail server or the user mobile telecommunications terminal is modified, which enables to keep coherence in identical information in both voice mailboxes of the voice mail server and the user mobile telecommunications terminal.