A multi-user telephone system composed of a plurality of user networks installed at the same general location. Each user network has a different telephone number and a plurality of VOIP extensions each having a different extension number. A server, upon confirming the address of an outgoing VOIP signal as an address of an intended recipient of the outgoing VOIP signal, permits the outgoing VOIP to be conducted to the internet. The VOIP extensions also can develop outgoing PSTN signals for transmission via a public switched telephone network. The server, upon detecting a PSTN outgoing signal, permits the outgoing PSTN signal to be conducted to a public switched telephone network. The server also confirms that the address of an incoming signal, from the internet or from a public switched telephone network, is an address of an extension in one of the user networks.