Verifying becomes a bit trickier when the company has a published phone directory instead of an on-line version. People get hired; people leave; people change departments, job positions, and phone numbers. The hard-copy directory is already out of date the day after it's published, even before being distributed. Even on-line directories can't always be relied on, because social engineers know how to modify them. If an employee can't verify the phone number from an independent source, she should be instructed to verify by some other means, such as contacting the employee's manager.