by non-intrusive coupling means, e.g. acoustic couplers

Substation equipment, e.g. for use by subscribers > Constructional features of telephone sets > Combinations with auxiliary equipment, e.g. with clocks or memoranda pads > by non-intrusive coupling means, e.g. acoustic couplers

Substation equipment, e.g. for use by subscribers (subscriber services or facilities provided at exchanges H04M3/00; prepayment telephone coin boxes H04M17/00; current supply arrangements H04M19/08) > Constructional features of telephone sets > Combinations with auxiliary equipment, e.g. with clocks or memoranda pads > by non-intrusive coupling means, e.g. acoustic couplers