A unified web-based voice messaging system uses an application server, configured for executing a voice application defined by XML documents, that accesses subscriber attributes from a standardized information database server (such as LDAP), and messages from a standardized messaging server (such as IMAP), regardless of message format. The application server, upon receiving a request from a browser serving a user, accesses the standardized database server to obtain attribute information for responding to the voice application operation request. The application server generates an HTML document having media content and control tags for personalized execution of the voice application operation based on the attribute information obtained from the standardized database server. The application server also is configured for storing messages for a called party in the standardized messaging server by storing within the message format information that specifies the corresponding message format. Hence, the application server can respond to a request for a stored message from a subscriber by accessing the stored message from the standardized messaging server, and generating an HTML document having media content and control tags for presenting the subscriber with the stored message in a prescribed format based on the message format and the capabilities of the access device used by the subscriber.