This is before my time also but I do have some info for it. There should be a multi button base on the bottom of it.

Executone Intercom Model 356. Unit is a Central Control Master Station with tube amp from the 1930's. This early model executive station was used for direct 2 way conversation within a building. There are 8 bakelite push button selectors including a white cancel button. Two toggles are also bakelite. Right toggle is the on / off volume control. Left toggle is a talk lever. Features are "privacy features, stand by silence, executive right of way, auto busy signal and pilot light indicator". Cabinet is wood with a walnut veneer. Unit wires up with a bundled cloth covered cable that leads to a metal connections box with 6 separate terminals. Model 356 has a 2 1/2 watt booster amplifier.

Merritt

Business Telephones & Equipment + Commercial Audio/Video Products
Commercial Communications . . . Turner, Maine
If it was built after 1980 don't expect it to work right.