Abstract: In a cordless key telephone system for servicing separate service zones (3.sub.1, 3.sub.2), a cordless station (5) establishes a two-way radio channel with an access unit (4) of the service zone in which it is located, and constantly monitors the field intensity of the established channel and transmits a zone switching signal when the field intensity is below a specified level as an indication that the cordless station is leaving a first zone (3.sub.1) and entering a second zone (3.sub.2). A main controller (2) establishes a switched connection between exchange lines (6) and the access units (4). In response to the zone switching signal from a given cordless station via the access unit of the first zone, the main controller holds an exchange line (6.sub.i) that is connected to the access unit (4.sub.j) of the first zone through a first switched connection, and establishes a second switched connection between the exchange line (6.sub.i) and the access unit (4.sub.

Abstract: In a cordless key telephone system in which radio-frequency connections are established between exchange lines and cordless stations in response to a call request, a ringing signal is transmitted in response to an incoming call by containing in it the identification of the line at which the call is terminated. Each cordless station has an array of line keys associated respectively with the exchange lines and an array of line indicators associated respectively with the line keys, and a memory for storing tenant data indicating the lines to which the cordless station is authorized to access.

Abstract: In a cordless key telephone system for covering multiple service areas, access units are divided into groups corresponding respectively to the service areas, the access units of each group being located in the corresponding service area for broadcasting a recurrent sequence of address signals on a two-way radio control channel and carrying speech signals on an assigned two-way telephone channel. The access units of each group has a uniquely assigned control channel different in frequency from the control channel of the other group. Cordless stations are switchable to the control channel of a first group of the access units for detecting an address signal and subsequently switchable to the control channel of the access units of a second group if the address signal is not detected in a first sequence for detecting the addressed signal in a second sequence.

Abstract: In a cordless key telephone system, access units are located in groups corresponding to service areas for broadcasting radio signals on a control channel or on an assigned speech channel to cordless stations. A main controller selects one of the access units for each service area in response to an incoming call from the switched telephone network and sends a first alert signal to the selected access units to cause them to broadcast a recurrent sequence of second alert signals containing the identifiers of standby cordless stations. The second alert signal is received by each standby cordless station and an ACK signal is transmitted if the received signal contains its identifier. The ACK signal is copied by each access unit for transmission to the main controller, whereupon it returns a proceed-to-assign signal if the number of the received copies of the ACK signals is equal to the number of all standby stations.