Abstract: An Active User Registry system comprises a database which is integrated with the POTS network and a packet network (such as the Internet, or a corporate intranet). Integrating AUR with the POTS network and a packet network exploits the outstanding strengths of both of its constituents, such as the low-latency, high reliability, moderate fidelity real-time voice telephony provided by the POTS network, and the point-and-click access to distributed databases with excellent search capabilities provided by a packet network, such as the Internet (including those made available using browser technology in conjunction with the World Wide Web). The AUR database contains a dynamic data structure (such as a linked list or a hashed table) of all the ways in which one or more users can be reached via some type of communication network (e.g., through the POTS network or a packet network, or both).