Abstract: A multiplicity of subscriber lines, originating at telephone stations equipped partly with dials and partly with keyboard-controlled multifrequency generators, are connected to pulse-responsive selection equipment by way of switching circuits which are under the control of respective key-signal detectors. Upon the operation of any multifrenquency generator, the latter emits a key signal which actuates the associated detector to switch that line to a conversion network wherein the incoming frequency combinations are translated into binary codes which are stored in a dynamic memory whence they are read out into an available binary/decimal converter. The stored binary codes are accompanied by a line address which enables a coupler to reinsert the selection signals, in the form of digital pulse trains, into the correct line with the aid of an associated interface unit.