A distributed control switching system (100) where calls, to and from a directory number that is shared by a key-system group (180) of terminals, are processed cooperatively by multiple, distributed control unit (111, 121, 131, 141) but in response to busy/idle data (126) for the shared directory number (DN2) stored advantageously by only a lead one (121) of the control units. In addition to processing a call, for example to complete a connection to or from one (e.g. 181) of the terminals of the group, the multiple control units also cooperate as the call progresses to inform each of the group terminals (181, 182, 183, 184, 185, 186) of the call status as though the terminals were connected in parallel to a central office line as in an electromechanical key system.