IP phone system

Disclosed is an IP (Internet Protocol) phone system that performs communication through packet exchange by VoIP (Voice over IP) and ensures the use of child terminal devices which are cordless telephone terminals. In the IP phone system, a computer device having an H.323 gate keeper function, a plurality of computer devices having a protocol conversion function and IP phones are connected to an IP network, identifiers of child terminal devices are respectively registered in the latter computer devices. When a Piconet of a communication link among the computer devices and the child terminal devices is formed, one of the child terminal devices makes a call to a desired terminal and executes voice communication over an IP network.