The old kiosks with button A and B had an emergency button on the wall at the back of the kiosk. I remember pressing it as a young lad to tell the operator a joke. She did not appreciate it.
I think you put your money in then asked for the number, when the other end answered you pressed button A otherwise the person at the other end could not hear you. Pressing button A dropped the coins into the phone, button b was for coin return if nobody replied.
Now heres a question for the old timers, in the days of old round pin plugs - 2 amp, 5 amp, 13 amp, with unshuttered sockets, there was a dual tariff. The 2 amp sockets were wired to the lighting circuits. I think lighting was cheaper per unit than power but a friend disagrees and says it was the other way round. Anybody know for sure? ( and yes we do have some sad arguments)