Editing Subscriber trunk dialling (section)

{{short description|Telecommunications technology and telephone numbering system}}
{{for|a North American equivalent|Direct distance dialing}}
{{Use British English|date=July 2020}}
{{more citations needed|date=December 2011}}
'''Subscriber trunk dialling''' ('''STD'''), also known as '''subscriber toll dialing''', is a [[telephone numbering plan]] feature and telecommunications technology in the [[United Kingdom]] and various [[Commonwealth of Nations|Commonwealth]] countries for the dialling of [[trunking|trunk calls]] by telephone subscribers without the assistance of [[switchboard operator]]s.

Switching systems to enable automatic dialling of long distance calls by subscribers were introduced in the United Kingdom on 5 December 1958. The system used area codes that were based on the letters in a town's name. A ceremonial first call was made by Queen [[Elizabeth II]] from [[Bristol]] to [[Edinburgh]].<ref>{{Cite news |url=https://www.telegraph.co.uk/technology/connecting-britain/international-subscriber-trunk-dialling-introduced/ |url-status=deviated |archive-url=https://web.archive.org/web/20170311181802/https://www.telegraph.co.uk/technology/connecting-britain/international-subscriber-trunk-dialling-introduced/ |archive-date=11 March 2017 |title=International Subscriber Trunk Dialling introduced |newspaper=[[The Daily Telegraph|The Telegraph]] |date=10 March 2017}}{{cbignore}}</ref>

A similar service, built on [[crossbar switch|crossbar]] equipment, using regionally structured numbering, rather than [[alphanumerics|alphanumeric]] codes, was experimentally introduced by [[Minister for Posts and Telegraphs|P&T]] in Ireland in 1957, with the first services being in [[Athlone]]. A full service was rolled out in 1958, initially to exchanges in [[Cork (city)|Cork]] and then [[Dublin]] and its hinterland, and gradually to all areas with automatic exchanges.<ref>{{Cite web|url=https://www.oireachtas.ie/en/debates/debate/dail/1959-07-15/33/|title = Committee on Finance. - Vote 55—Posts and Telegraphs. – Dáil Éireann (16th Dáil) – Wednesday, 15 Jul 1959 – Houses of the Oireachtas}}</ref>

The term 'STD call' was once commonly used in the UK, Ireland, [[Australia]], [[India]], and parts of [[Southeast Asia]], but it may be considered archaic today, or possibly even no longer be understood. Other less technical terms like 'national calling,' 'long distance calling' and so on are now more commonly used. The distinction between local and long distance / STD calls is also no longer relevant to many users, as calls are charged at flat or bundled rates. It is also necessary to dial area codes on some calls, especially from mobile phones, so they are considered part of the number.

Terms such as 'area code', 'prefix' or 'national dialling code' tend to be used in place of 'STD code' in the UK and in Ireland.