In this project, I show you how you can make a simple intercom system from a pair of old corded telephones. The phones already have all the circuitry that is needed for processing a voice call. All you need to add is a 9 volt battery and a resistor. This is an easy electronics project for beginners and it is great to do with children. Try it out and have fun.
Here’s the full build on MAKE: Projects–http://makezine.com/projects/simple-intercom-from-a-pair-of-old-corded-phones/ and on Instructables: