Null phone

The null phone is a computer program that sends signals down a long phone line to take control of a person's phone for prank purposes. After hours, you substitute the normal phone plug for the one leading to your computer. This would not be too difficult in most offices, with long lines running under the floor.

Once revised this line could be used for any number of fun pranks. It could make the phone ring one long uninterrupted ring, or short tiny occasional rings. People dialing out would hear a normal ringing sound - then could optionally be connected to their own voice mail, hear annoying long automated messages about numbers not being in service or even be connected directly to the prankster, who would ad lib in a falsetto voice. Occasionally, the program might even allow a phone call to get through, maintaining the illusion.