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 was a receptionist about five years ago for a small office. I would check the voicemail in the morning and write these out and leave them on the recipients desks before they arrived in the morning. Then I would use them throughout the day if the person was in an appointment when a call came in for them. It was an alternative medical office and whooo boy did people give me TMI, for the slip and for me personally.