A communications system featuring a remote security server is provided. The system allows the validation of requests for access to a communications network to be performed in a centralized security server. The use of a security server allows security features to be implemented, without the need to distribute a security algorithm to individual client devices. In addition, changes to the security algorithm can easily be made, because such changes need only be made in the security server itself, and in the communications server to which access is desired. The present invention is particularly useful in connection with communication services provided as part of a private branch exchange.