Subscriber Trunk Dialling (STD) is an obsolescent term for the UK telephone system allowing subscribers to dial trunk calls without operator assistance. A subscriber is someone who subscribes to, i.e. rents, a telephone line and a trunk call is one made over a trunk line, i.e. a telephone line connecting two exchanges a long way apart. Now that all calls may be dialled direct, the term has fallen into disuse.
The term Subscriber Trunk Dialling is, or was, also used in other countries such as Australia but the corresponding term in the US and Canada is Direct Distance Dialing.
In the UK, STD started when, on 5 December,1958, the Queen who was in Bristol dialled a phone call to Edinburgh ([1]). However, it was not until 1979 that the STD system was completed ([1]). The system required that each area have its own STD Code which could be dialled by subscribers, and although they are now officially called Area Codes, it is still common to see and hear the old term in everyday use.
The term was extended, when on 8 March,1963, London subscribers were able to dial Paris direct using International Subscriber Trunk Dialling ([1]).
http://www.btplc.com/Corporateinformation/BTArchives/history/Eventsintelecommunicationshistory.htm
References
http://news.bbc.co.uk/onthisday/hi/dates/stories/may/21/newsid_2510000/2510289.stm
- Archive news article from the BBC on the introduction of Subscriber Trunk Dialling.
- Article detailing how the original STD Codes were allocated.
