On 25th of September 1956 the first Trans Atlantic telephone cable (TAT 1) came into operation linking up Newfoundland, Canada to Oban, Scotland.
A marvel of communications engineering, the cable was able to carry 35 telephone calls at one time.
Between 1955 and 1956 two cables had been laid for calls going in each direction.
The total cost of the project was £120million split between the General Post Office of the UK, the American Telephone and Telegraph company, and the Canadian Overseas Telecommunications Corporation. The share split in the scheme was 40% British, 50% American, and 10% Canadian. Wikipedia
TAT-1 carried 588 London-US calls and 119 London-Canada calls in the first 24 hours of public service.
This is a short film about TAT 1
And this link takes you to a longer film about TAT 1 and its development.