Sir,
I want to pass along a recommendation for field telephones. Coleman’s Military Surplus is selling Swiss army surplus field telephones (made by Ericsson) for $19.95 plus shipping. I have purchased some of these and have good luck with them.
They use a crank for ringing the bells and “D” cell batteries for voice transmission. They can also be hooked up in a common battery / switchboard set up if a person is lucky enough to have one. – Matthew in Kansas City, Missouri