An intercom can be a useful tool or a fun toy. In this project, I am going to show you how to make a simple intercom using a pair of old corded telephones. This is an easy electronics project that is great for beginners and fun to do with children.
Read More: http://www.instructables.com/id/Simple-Intercom-From-a-Pair-of-Old-Corded-Phones/
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. Try it out and have fun.
Here's the full build on MAKE: Projects--http://makezine.com/projects/simple-i... and on Instructables: