Patent ID: 7738649

Claim:
A computer system comprising: a private branch exchange (PBX) that connects calls among a plurality of extension lines or among extension lines and external lines and that is connectable to another terminal device; a management server; and a terminal device that is connectable to the PBX and that is connectable to the management server via a network, wherein the PBX includes: a line controller that controls connection or disconnection with respect to an incoming call or an outgoing call from a public network or a private line via an external line; an extension controller that controls connection or disconnection of an extension line and the call; an interface that connects the PBX to the terminal device; a memory that stores a control program of the PBX and identification information to identify the PBX from another PBX; a decoder that decodes an enciphered file serving as enciphered authentication information; a comparator that compares the identification information to the enciphered file decoded by the decoder; and a controller that controls the PBX based on the stored content of the memory, the terminal device includes: a local interface that connects the terminal device to the PBX; a network interface that connects the terminal device to the management server via the network; a reader that reads the identification information from the PBX; a memory that stores the identification information, the enciphered file, and the control program of the terminal device; and a terminal controller that controls the local interface, the network interface, and the reader, the management server includes: a network interface that connects the management server to the terminal device via the network; an authenticator that receives a request for authentication when the terminal device logs in the management server; an issuer that issues the enciphered file enciphered according to the identification information received from the terminal device after the authentication of the authenticator; and an installation date management database that stores a date, on which the enciphered file is issued, in correlating with the identification information, the PBX further includes a function activator that assigns whether to restrict or activate a part or all of operational functions of the PBX, and the controller controls the function activator based on the comparison result of the comparator to assign whether to restrict or activate the part or all of the operational functions of the PBX.