In an emergency backup telephone system, members of an enterprise use their personal computers to log into an emergency communications web page. Upon logging in, software that enables the personal computer to act as a webphone is automatically downloaded. This software allows a person to initiate a call from personal computer to a conventional PSTN number destination using a PSTN gateway, or to another party's computer at a specified URL using VoIP telephony. Upon logging in, an authoritative index of employees reachable via the backup system updated to include information such as a phone number and/or IP address where the member can be reached in order to allow calls originating from the PSTN to be routed to the member's computer. The index is made available to other members of the enterprise via the enterprise's intranet, and, in some embodiments, to the public via a web page on the internet and/or email.