Bell “Gallows-Frame” telephone
Alexander Graham Bell's original telephone prototype used a single magneto-based device as both transmitter and receiver. The user spoke into the single orifice, and put the device to their ear to hear the response.
The device, which gets its nickname from its elegant mahogany frame, was the first with which Bell demonstrated transmission of voice-like sounds. Intelligible speech would be transmitted by Bell with a redesigned unit the following year.