Abstract: The electrical signals generated by an audio source are applied to a plurality of series connected light emitting diodes which are illuminated responsive to the signals. The light emitting diodes are respectively optically coupled to individual phototransistors, each of which is connected in series with a resistor across the hold impedances of the hold circuit of an individual telephone line. When one of the hold impedances is connected across its associated telephone line, line current flows through the hold impedances. Line current also flows through the parallel resistor when the phototransistor is turned on responsive to the illumination of its associated light emitting diode. The phototransistor thus modulates the current flow through the hold impedances to provide an audio signal output on the held line.