One of the subjects 12/30/13 guest Cal Cooper has studied is a very eerie occurrence that a number of people have reported. They actually receive a phone call from someone who has died, usually a close relative or friend. The telephone ring is said to sound somewhat abnormal and the connection may have static. However, the deceased's voice is clearly recognizable though it usually fades away or ends abruptly.
Most calls are from the very recently deceased (within 24 hours of their passing) and the purpose behind them seems to vary. They may wish to impart a final message, issue a warning or give needed information. One of the most well known cases, was when actress/director Ida Lupino got a call from her father (who had died six months earlier) telling her where to locate some estate documents.
Interestingly, Thomas Edison, the son of spiritualist parents, started but never completed a telephone he envisioned would connect the living and the dead.
Source: Harper's Encyclopedia of Mystical and Paranormal Experience by Rosemary Ellen Guiley