wasn't it 161?
I remember being in one of the side rooms in Rhyddings with a girl from my year waiting for the careers teacher( it was next to what was then the 5th year common room), and she knew how to "click" the receiver to dial the number. ( The phones were internal ones with no buttons on ). You also have to remember this was long before "tone dialling"! I was mightily impressed but she was well out of my league ( And I only had eyes for Amanda Barber back then!
)