Patent ID: 8000463

Claim:
A telephone system, comprising: a first phone terminal belonging to a private communication network; a second phone terminal belonging to a public communication network; a transit device which connects the private communication network to the public communication network; and a call control device which controls a call between the first phone terminal and the second phone terminal, wherein the private communication network includes: network equipment; a first certification processing unit which is disposed in the network equipment and performs certification proxy processing to certificate whether or not the first phone terminal should be connected to the public communication network; and a notification processing unit which notifies the result of the certification proxy processing to the call control device when a call connection request to form a communication link between the first phone terminal and the second phone terminal occurs, the public communication network includes a second certification processing unit which performs certification processing of the network equipment, and the call control device forms the communication link in response to the call connection request if the notified result of the certification proxy processing shows a success and the certification processing of the network equipment shows a success.