Probably people only know that number because they have the money from suckers who use their directory numbers to do all that advertising on TV.
I had an elderly neighbour who knew no better than using BT Directory and after getting extra billing of £28 twice but after mentioning his problem on here I was given a choice of 3 numbers that ranged from 32ppmin. to 41p for whole call and a FREE but very busy number that I warned him off.
I duly passed these on to him, resulting in a very happy bunny. I know that these charges will be altered next year and when I find out I will be Updating him.
Thanks the people who provided those numbers.