I'm not sure how well-developed the research behind the theory is, but I have personally heard one of these "voices."
My friends and I do ghost hunts from time to time, visiting graveyards and such and taking pictures, recording "voices," what have you. One night on our way out, my two friends were talking about going to one particular cemetery.
When we got into our car a few minutes later and began listening to the recording, at the very end when we were talking about going to the other cemetery, there is a clear whispering voice saying "Take Me." We went over it many times, and we cannot explain the voice.
A good show about ghost hunting is Ghost Hunters on the Sci-Fi channel. It is fun to watch them investigate certain sites and how they determine if their evidence is sufficient to declare a place haunted. More often than not, they throw away most of the potential evidence, and only rarely are willing to actually say if a place is haunted.