This was used in the recent rescue in Wales [0]. I seem to recall a colleague telling me years ago (in about 2000) that he got stuck in a cave once (somewhere in South Wales I think) due to unexpected rain causing flooding and there was a phone available that could be used to request rescue (or to tell people you were going to sit it out).

[0] https://www.bbc.co.uk/news/uk-wales-59219380