At first, callers could not dial another number directly, but had to be connected by a switchboard operator. Switchboards often used a cord system, which required operators to move a plug and cable from one point to another to make the connection. Operators had to be well spoken and were trained to use approved phrases only.
As the United Kingdom exchange system became more automated, there was less need to dial into an operator switchboard. Cordless exchanges were first introduced in the mid-1950s, and from the 1970s, digital electronic switching began
1901 - 1925