See attached from BT's 1989 North of Scotland Telephone Directory of a number it still wasn't able to dial. It was in a croft on the Isle of Harris with no road access until 1990. Only accessible by a five mile footpath over the hills. It was used as an 'attended call office' where you made the call, then the attendant collected the money from you once advised of the cost by the operator!.
There is an excerpt from a BBC programme 'The Secret Life of Telephone Numbers' (of about 2005) which is about the number which can be heard by dialling 01859 (Harris) 598 001 ( Rheinigidale 1
) - a 'normal geographic number' so should be in your 'free calls' package.