How to dial on S.T.D.
The telephone dial was as shown to the left. Each digit could represent a letter or number, except '1' which was a digit only. To dial a trunk call using S.T.D. you needed to dial 'O' first. This previously dialled the operator. The operator then became '100'. Conveniently the letter 'O' and zero were the same. The next digit depended on where you were dialling. If you were dialing a major city - London, Birmingham, Edinburgh, Glasgow, Liverpool or Manchester you needed to dial the code for that area. These were known as 'Director' areas. Before S.T.D. if you lived in a director area you could dial other numbers in the director area using the lettered exchange followed by the number. For example MAYfair 1240 was MAY-1240. That's 629-1240. To dial on S.T.D. from outside London you needed to dial 'O' followed by '1' - the code for London followed by MAI-1240 so
The other director areas could be dialled by 'O' followed one of the following codes:
So that's 'O'-21 for Birmingham or 021 - sound familiar?
What about the rest of the country?
You needed to dial 'O' again, but followed by two letters and a number representing the area into which you were dialling. Followed by the number that you were dialling.
Your guide to vintage and retro