PBX-integrated unified messaging capabilities are provided via a switched backbone (such as the Internet) without having to install or deploy on-premise unified messaging equipment. A Corporate Communication Platform ("CCP") typically located within a corporate subscriber's premises is integrated with the corporate subscriber's private branch exchange ("PBX") system and coupled to a switched backbone, such as the network commonly referred to as the Internet. The CCP comprises a local mailbox database that temporarily stores voice messages and/or facsimile transmissions for and transmits messages to individual subscribers associated with the corporate subscriber. A CCP forms part of a wide-area unified messaging system, and connects to this wide-area unified messaging system via the switched backbone. The wide-area unified messaging system also comprises one or more System Communication Platforms ("SCP"). Each SCP in the wide-area unified messaging system may be located anywhere in the world that is accessible via the switched backbone, and may include a PSTN interface and/or a permanent mailbox database. Each SCP may also comprise a HTML Web server and/or an e-mail server to provide unified messaging capabilities. Each CCP is assigned to a SCP, and is slaved to the assigned SCP, such that the local mailbox database in the CCP is synchronized with the mailbox database of the SCP assigned to the CCP. Voice and fax messages received at the customer premise via the PBX are captured and stored at the CCP, which promptly uploads copies of the messages to its assigned SCP via the Internet. Once messages are received at the SCP, the individual subscriber can retrieve these messages via a web browser program, e-mail client program and/or the PSTN interface of the SCP. Conversely, copies of voice and fax messages received by the SCP via its PSTN interface are also promptly downloaded to the appropriate CCP, and the individual subscriber may retrieve these messages from his or her extension off the PBX.