At a business, a secretary, almost always a woman, would answer the phone for all calls. There were no direct lines into anyone. If you were in she would transfer the call to your office. If you were out she would use this pad to take messages. When you came back in to the office you would always stop at the front desk and you would be handed your messages.
I used to flip them over, the back was plain, and write DAVE RANG.
“Dave who ?” “Didn’t say” “Did he leave a number” “No” “What was it about” “He said you know what it’s about”