Patent ID: 7580422

Claim:
An Internet Protocol (IP) phone system in which packets of call setting or sound signal are transmitted, and a voice telephone call is performed, comprising: a local IP network which has a different IP address system from a global IP network, and is mutually connected with another local IP network via the global IP network; an IP phone device which has a phone number, and is connected to the local IP network; and an IP address translation device which is connected to the local IP network, assigns a local IP address and a global IP address corresponding to the phone number of the IP phone device, and retrieves the local IP address and the global IP address assigned to the phone number of the IP phone device, wherein: when a transition from a waiting state to a calling state of the IP phone device is detected, the IP address translation device assigns the global IP address corresponding to the phone number of the IP phone device thereto, in the calling state, the IP phone device transmits and receives packets of call setting or sound signal based on the global IP address assigned to the phone number of the IP phone device with another IP phone device provided in another local IP network, and when the calling state is finished, the IP address translation device retrieves the global IP address assigned to the phone number of the IP phone device.