Courtesy of Allen Miller
Allen adds: "Wayside phones were able to connect to either the block phone circuit, to ring up the depot, section foreman, substations, etc. using the ring code chart that was normally posted inside every box, or written in pencil on the inside wall or door panel.
Or, with the throw of a knife switch, you could contact the train dispatcher direct on the "DS" phone circuit. Some would turn the crank handle, making one l-o-n-g ring, that would just make a rumbling sound on the dispatcher's phone, but may have actually rang a bell in the dispatcher's office, I'm not sure about that. Anyway, it was not necessary as it was an open circuit and one only needed to press the talk button on the lineside phone and ask "Dispatcher?" for him to answer.
On the Coast Division, although they were gradually weeded out over the years, there were still many of these phones in operation right up until the end in 1980 on the main line. Most branch lines were phased out by the mid-1970's, replaced in section houses by commercial telephones where service was available."