Simple signaling without co-stimulation allows the cell to recognize the primary signal as self and not ramp-up responses for future responses as well.
In the decades following, pulse dialing was gradually phased out as the primary signaling method to the central office, but many systems still support rotary telephones for backward compatibility.
Light is the primary signal that affects this 24-hour biological cycle and travelling long distances means our bodies are exposed to light and dark when they aren't expecting it.