Because it was put in my head by @snathe and @fintanbear, here's a short thread of Post Office Telecommunications trimphones, starting in the Daily Mirror on 19 May 1977.

The Liverpool Echo, 15 October 1980

The Belfast Telegraph, 19 January 1970

A trimphone trimcrimewave in the Aberdeen Evening Express on 30 March 1976

And the pushbutton trimphone makes it debut in the Daily Mirror on 25 September 1978. If I'm not mistaken, 01-246 8071 is the number for the recipe of the day (daytime) and the bedtime story (after 6pm).