TELEPHONE SYSTEM, DOCK DEVICE, PORTABLE TERMINAL, AND METHOD FOR APPARATUS CONNECTION IN TELEPHONE SYSTEM

PROBLEM TO BE SOLVED: To use a portable terminal having a display element with a relatively large display screen in a telephone system formed in a company or the like for a wide range of effective use.SOLUTION: When a cellphone terminal 5 is connected to an external terminal of a dock device 4, a terminal registration/deregistration processing section registers the device itself in a SIP server 1 as a subordinate telephone terminal. The dock device 4 connects a channel (communication line) to a desired opposite party in response to an incoming call or by making a call, so that a handset 406 can be used for a telephone call. The dock device 4 controls the cellphone terminal 5 connected thereto with a display control message from an internal display control message providing section to use it as a display device of the telephone terminal comprising the dock device 4 and the cellphone terminal 5.