When Edison joined the legions of the dead, he left behind no schematic for his envisioned ghost box, the telephone to the dead. There are however some who claim to have been in contact with Thomas Edison via the very same technology he never actually completed.
Their work is available in Phone Calls from the Dead
Case of Fredrich Juergenson
Fredrich Juergenson, a Swedish artist and performer was recording sounds of nature, birds. When he played back the recordings he heard his mothers voice saying 'Friedel, my little Friedel, can you hear me?' and 'Friedrich, you are being watched' . As per Juergenson when he realized what he had recorded he attempted to re-contact his Mother and other deceased family members
Juergenson joined his Mother on the "other Side' in 1964 but left behind many tapes in which a multitude of voices can be heard. Radio and Audio experts, were unable to pin point a reasonable scientific explanation for the Juergenson phenomena.
Latvian psychologist, Dr. Konstantin Raudive, read of the Juergenson Phenomena and tested Juergenson's techniques. The end result was many voices, including that of what he believed was his deceased mother. Raudive chronicled his work in Breakthrough: An Amazing Experiment in Electronic Communication with the Dead.
In addition to the recordings Juergenson left behind two books on the subject "Voices From the Universe" and "Radio Contact with the Dead." English Translations unavailable.
Starting in the 1960s paranormal investigator Marcello Bacci claimed to be 'dialing in' the voices of the dead using a modified radio.
In 2002 Italian Physicist Prof. Salvatore Mario Festa, attempted to expose Bacci as a fraud, but was unable to. Festa came out a believer as he witnessed the phenomena and was unable to uncover any 'hanky-panky'. He did however write in his report ... "One thing is certain: the voices phenomenon happens only in the presence of Bacci. Then what is the role of the Medium? ..." 
In 2004 Festa attended another session along with a group of seasoned investigators from Italy, Portugal and the UK. They investigators included scientists from various relevant disciplines. They too believe that they eliminated the possibility of fraud. 
William O'Neil and George Meek
In 1979 the duo constructed what they called the Spiricom, a version of a Ghost Box". O'Neil claimed to have received his instructions from a scientist who had died a few years earlier. In 1982, O'Neil stated that he was able to conduct conversations with spirits through his device. Oneil's specs were provided for free to any who wanted them, but failed to meet the requirements of scientific validity. The results he claimed to have achieved could not be duplicated by all who tried.
George Meek, O'Neil's partner, attributed the inability of others to replicate it to O'Neil's mediumistic abilities forming part of the loop that made the system work. This claim would tie in with the investigators of Marcello Bacci who stated "One thing is certain: the voices phenomenon happens only in the presence of Bacci. Then what is the role of the Medium? ..."
In 2002 Frank Sumption introduced his version of the Ghost Box - commonly known as the Frank Box. It is basically a white noise generator and AM radio receiver modified to sweep back and forth through the AM band to select split-second snippets of sound. Skeptics claim the Frank Box relies on coincidental noises and pareidolia. Pareidolia is a psychological effect in which a misconception is derived from an obscure stimulus and interpreted by the Brain as something meaningful, clear and distinct.
In 1901 Anthropologist Waldemar Bogoras used a phonograph to record the chanting and language of Siberian tribes and unexpectedly recorded something quite bizarre. While recording a shamans ritual he also recorded voices taht were not present when he had made the recording, or at least they were not perceived by him.
The recordings are currently the property of NY Museum of Natural History and only the high priesthood of the Scientific realm are permitted access.
Minnesota State University Researchers have been unable to explain them, and it remains a credible piece of evidence in support of Electronic Voice Phenomena.
In the first session an Americanized English speaking voice is heard - mimicking the shaman - the voice seems annoyed, as if it resents being drawn into the shamanic ritual - but culminates with the English speaking voice laughing.
Another session records a wolf clearly howling as the shaman beat his drum and chanted.
The Bogoras incident would also tie in with the hypothesis of a 'medium' personality being present - the shaman being the medium.
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Footnotes and References
1. A PARTICULAR EXPERIMENT AT THE PSYCHOPHONIC CENTRE IN GROSSETO, DIRECTED BY MARCELLO BACCI
2.REALITY OF INSTRUMENTAL TRANSCOMMUNICATION VOICES SCIENTIFICALLY DEMONSTRATED