The Great Gray Plague — Raymond F. Jones

On the surface, James Ellerbee was a crackpot with an impossible invention: a crystal cube you could hold in your hand that allowed instant communication with anyone on Earth. But the inventor came with affidavits, signed and notarized, from three unbiased witnesses: the Fire Chief, the Chief of Police, and the Community Church Pastor of Redrock... Originally published in Analog Science Fact and Science Fiction, edited by John W. Campbell, Jr.