Businesses very commonly allowed customers and passersby to use business phones. Some even had telephones out on the counter or in some other convenient locations for customers to use, even though the telco tariffs prohibited this. Telephone calls were measured rate only in a small part of the United States, and there was little or no incremental cost for a customer to use the phone in the vast part of the U.S.A. that had flat rate service.
The reason for prohibiting employees from using employer lines, then as now, is primarily because the loss of productivity when the employee carries out personal activites when he or she is supposed to be doing the employer's business.
Wes Leatherock snipped-for-privacy@aol.com snipped-for-privacy@yahoo.com