Method and apparatus for correlating a unique identifier, such as a pstn telephone number, to an internet address to enable communications over the internet

A directory service, containing unique identifiers (e.g., telephone numbers) and related Internet address(es), accessible through the Internet. An Internet-enabled communication system, such as IP-PBX or voice mail system, accepts a telephone number as a destination address. It then contacts the directory service and requests the Internet address related to that telephone number. The communication system uses the Internet address to set up a delivery path via the Internet to the destination. Thus, all time-dependent charges normally associated with message delivery by the telephone network can be avoided.