Button telephone system which displays line status information

Claim 1

A button telephone system comprising a parent telephone set provided with an exchange function, and a child telephone set, said parent telephone set being connected to a public telephone line through a channel line and being connected to a host private branch exchange through said channel line and a data communication line, said parent telephone set including: a public telephone interface section having a line control means for transmitting a second voice signal, which is transmitted from said child telephone set, to said public telephone line or an extension telephone line of said host private branch exchange through said channel line, and a first communication control means for performing data communication with said host private branch exchange through said data communication line; second communication control means for performing radio communication with said child telephone set by modulating a first voice signal, which is transmitted from said public telephone line or said extension telephone line of said host private branch exchange through said channel line, by modulating a first control data into a first radio wave to transmit said first radio wave to said child telephone set, and by receiving a second radio wave, which is transmitted from said child telephone set, to demodulate a second control data and said second voice signal from said second radio wave; a channel switch provided between said line control means and said second communication control means, for connecting and releasing a voice channel between said public telephone interface section and said second communication control means; and line condition display conversion means for converting an external telephone line condition signal into a line condition display signal which is transmitted to said child telephone set, said external telephone line condition signal being transmitted from said host private branch exchange through said data communication line and said first communication control means; wherein when communication request data are transmitted from said host private branch exchange to said first communication control means through said data communication line, said parent telephone set enters a mode in which said parent telephone set operates as an extension telephone terminal of said host private branch exchange, and said second communication control means modulates said line condition display signal into said first radio wave to transmit the modulated first radio wave to said child telephone set, and said child telephone set including: line condition display means; child telephone set control means for controlling said line condition display means to display a line condition in accordance with said line condition display signal transmitted from said parent telephone set; and an operation button used for operating said child telephone set.