An interesting thread. It's really discussing transcommunication, which sort of includes EVP, although TC is supposed to be communication in real time.
The book "The Ghost of 29 megacycles" might appeal to some readers of this thread. Google "George Meek" SPIRICOM, METAscience, and "Bill O'Neil". This bunch claimed that real-time communication was established with deceased Dr. George Jeffries Mueller - a NASA scientist.
Plot spoiler; it was almost certainly a hoax, although why anyone would perpetrate such an elaborate one escapes me. The fact that O'Neil was diagnosed as a schizophrenic and had access to an early artificial larynx doesn't strengthen their case!
But hey, read up on all the versions of what happened and draw your own conclusions.
A "Yes" "No" device should surely be available by now - operating on random noise, or something much more sophisticated and sensitively balanced so that just the gentlest of nudges by a sprit would tip it into the correct state.
As far as I can tell Spirit Boxes and similar rely on wishful thinking and audio pareidolia, although I have heard of claims they have produced relevant names and data. How does that work...?