Electronic voice phenomena (EVP) and instrumental transcommunication (ITC) utilise modern electronic media such as radio, television and computers to receive messages from the spirit world.
Popularised by Konsantine Raudive and utilised more recently by Mike Kelley and Scanner, among others:
Video testemonial: http://www.youtube.com/watch?v=iSSqQ_gJlXU
Slideshow with audio clips: http://www.worlditc.org/t_01_introduction_01.htm
Try it yourself: http://paranormal.about.com/od/ghostaudiovideo/a/aa072604.htm