Here is a neat little project using the free program Skype and an old cordless phone. For those of you unfamiliar with Skype, I will school you. Skype is a free program that allows users with broadband connections to make free phone calls over the internet. Normally one would use a headset or a microphone and the speakers on the PC to send and receive voice, but by using an old phone and modifying it, you can make regular calls using the handset like a normal call.
Check it out here.