ATEA 1949 Series telephone.

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Picture and diagram:

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The blinkers/indicators tells if the 2 trunks are busy or not. The 5 middle buttons are for dc signalling to max 10 other phones. (Up or down on each button) When you go off hook you are connected to the common local phone line. pressing one of the 2 trunk buttons disconnects local line, and connects to trunk-line. pulling the same switch up, and the trunk-line are on hold, wile you talk to another ext. Putting the handset on-hook releases all connections, if not another phone has pressed the trunk line button. 
To each telephone it was a box with buzzers and relays, one place it was a main box with DC power supply.
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