With constant developments in mobile phone technology, we tend to take the humble landline for granted, and barely think twice about the ability to speak to someone on the other side of the the world.

However, just over a century ago, the telephone was at the forefront of cutting-edge technology.

The National Telephone Company arrived in Elstree in 1905, nearly 30 years after Alexander Graham Bell invented the telephone.

The company installed an exchange in a small cottage in Elstree, though its exact location is unknown. It was run by the cottage’s occupiers, a brother and sister called John and Annie Field.

The first resident to subscribe to the exchange was Lord Aldenham, of Aldenham House. Once an overhead line had been added to include the Borehamwood area, he was followed by the licensee of the Crown, a dog breeder in Theobald Street, and a surgeon in Allum Lane, Elstree.

In 1912, the National Telephone Company was taken over by the General Post Office (GPO), which operated exchanges in other parts of the country.

As the number of lines increased, it soon became necessary to expand the exchange, so it was moved to a house in Elstree High Street in 1921. The operator is said to have left at 10pm each night, but what happened to calls made after that time is a mystery.

Alan Lawrence, curator at Elstree and Boreham Wood Museum, said: “Before they even had an exchange in Elstree, there were trunk lines effectively going all the way from London.

“In those days, once someone was talking on one of those lines, that was one of the lines gone, so you had to wait for a line to become available.”

Telephones became increasingly popular and, by 1924, the exchange had 97 subscribers, rising to over 500 in 1939.

This expansion required another move, this time to the new post office in Borehamwood, which opened in 1935. A new automatic system was installed which could accommodate 750 subscribers’ lines, but could be extended to serve several times as many to allow for continuing growth in demand.

This was the first automatic exchange through which callers from central London could dial directly to phones in the area without having to go through an operator. Usually this was only possible for calls to neighbouring towns and villages, whereas a call made to a city further afield would have to be channelled through an operator.

Bob Mackintosh worked as a technical officer and line manager for the GPO and later British Telecom, now BT, and volunteers at Elstree and Boreham Wood Museum.

He explained once the exchange became automatic, there was no longer any need for operators. “It would have been virtually just a one-man operation,” he said. “They still kept a manual board going for anyone who dialled, but that was based at North Edgware Exchange.”

British Telecom took over the management of the telephone system from Post Office Telecommunications in 1981.

Reflecting on the changes in telephone equipment over the last century, Mr Mackintosh said: “In a hundred years, you could say that it’s gone from a little box to a huge piece of equipment then back to a little box, which is in the exchange now and is totally digital.”