Direct distance dialing

Direct distance dialing (DDD) is a telecommunications service in North America by which a caller may call any other subscriber outside the local calling area without operator assistance, DDD was introduced in the United States in 1951 with service from Englewood, New Jersey.

International Direct Distance Dialing (IDDD) extends the system beyond the geographic boundaries of the North American Numbering Plan (NANP).

Customers of the ENglewood 3, ENglewood 4 and TEaneck 7 exchanges, who could already dial telephone numbers in the New York City area, could place calls to eleven major cities across the United States by dialing the three-digit area code and the seven-digit directory number.

Montreal, Quebec, and Toronto, Ontario, in Canada, for example, had a mix of six- and seven-digit telephone numbers from 1951 to 1957, and did not have DDD until 1958.

For international dialing, Traffic Service Position System (TSPS) provided the extra computer power.

As this and other improved technologies became available, as well as Automatic Message Accounting (AMA) computers to process the long-distance records into customer bills, the reach of DDD was slow in the 1950s, but quickened in the early 1960s.

In the 1960s, with the domestic conversion still underway, plans were laid to extend Direct Distance Dialing beyond North America (including a number of the Caribbean Islands).

Some subscribers could already directly dial transatlantic telephone calls to certain destinations as early as in 1957 over the recently completed Atlantic cable to England.

Gateway offices were set up in New York, London and Paris, connected to the ordinary automatic toll network.

[citation needed] The new LT1 5XB switch on the tenth floor of 435 West 50th Street received new originating registers and outgoing senders able to handle fifteen-digit telephone numbers, with appropriate modifications to completing markers and other equipment.

[citation needed] Queen Elizabeth II inaugurated STD on 5 December 1958, when she dialed a call from Bristol to Edinburgh and spoke to the Lord Provost.