Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Publication of BE529412ApublicationCriticalpatent/BE529412A/xx
H04M9/00—Arrangements for interconnection not involving centralised switching
H04M9/002—Arrangements for interconnection not involving centralised switching with subscriber controlled access to a line, i.e. key telephone systems
H04M9/003—Transmission of control signals from or to the key telephone set; signalling equipment at key telephone set, e.g. keyboard or display equipment