This is how we used to phone people years ago. You would put 4d, proper pennies, in the slot and dial the number you wanted. When the person on the other end picked up their phone you would press button A. If they failed to answer you would press button B to get your money back. However it was almost impossible to pass a phone box and not going in to press button B in case the previous user had forgotten to retrieve his 4d.
The shelves used to hold 4 phone books listing all the local numbers.
A-D E-K L-R and S-Z. Later the yellow pages.