BATTERY INTERCOMMUNICATION TELEPHONES
"REPLY-AND-CALL" SUB-STATION AUTOMATIC
Pattern No. B620
Comprises the same parts as Pattern No. B615, but with the addition of a Wall Rosette and Cord.
These Sub-Station Instruments are suitable for use with any ordinary pattern Battery Intercommunication Telephone as Central Station Instrument,
but when so used the Sub-Stations cannot be switched through to one another.