William E Baker, Fritz E Froehlich, Hans G Mattes: Cordless telephone system. Bell Telephone Laboratories Incorporated, T H Jackson, H L Newman, June 26, 1984: US04456793 (168 worldwide citation)

The present key telephone system comprises cordless telephone stations (FIGS. 6 and 7) which communicate over a line-of-sight transmission end link (276 or 277). The system further comprises a central controller (101) for switching communications between the cordless stations and to the message netw ...