A real-time messaging system and method for a plurality of users that obviates the need to install specialized, dedicated software on user computers, and renders the need to become a subscriber of the system unnecessary. The real-time messaging system is a rules-based system that applies a set of rules and user attributes to the availability status of the users to facilitate effective real-time communications between the users. The system allows each user to indicate his or her on-line presence via a hyperlink embedded in and displayable on a web page, an e-mail message, or other hyperlink-supporting document. Each hyperlink is associated with a URL that points to a document such as a web page configured to initiate an on-line meeting or teleconference. A user who wishes to participate in an on-line meeting or teleconference selects a hyperlink corresponding to a particular user or user group, thereby initiating the desired on-line meeting or teleconference.