Call boxes used a series of electrical impulses to connect one person with another. They could be used to summon someone (they were popular ways to call for a servant in more affluent homes), but they also provided effective two-way communication. Railroads recognized this and placed call boxes alongside their tracks at convenient intervals between stations. This allowed conductors to have consistent communication outlets.
Installed in the train yards, at stations, and at various points along the track, on some stretches these call boxes were the only communication methods between trains and the rest of the world. The early call boxes worked in many respects as a telegraph system. As the telephone became more widespread, call boxes were retrofitted with "one-way" phones that would call out to the closest station. This allowed conductors immediate communication with the outside world and the ability to report on track conditions, call for assistance, or just pass a few minutes in conversation.
Today, call boxes can still be found on trains---only inside the cars. Call boxes are very prominent on subway and rail cars as a type of emergency intercom between the conductor and the passengers.
As electronic communication devices became more prominent and railroads began to modernize, rail-side call boxes have become a relic of a bygone era. You can still find call boxes along the side of the tracks, but they are rarely functioning and, instead, they stand as forgotten monuments to the glory days of rail travel.
