Do doctors wait until your appointment to deliver bad pathology results or do they call?

It depends on the office, and what their policy is. If the results are ready you can ask them for over the phone and see what they say. My office said they would phone me.

Why would they wait? If the news is bad, they would want to get back into the office for further tests and/or treatment ASAP.

if it's important, they'll call ASAP. they don't want their source of income dying...

Depends on the doctor. I have one friend who was told she had cancer over the phone. That shocked me. Another was told when she was the dr office

It depends on the doctor and the type of information.  For example, some blood test or infection results will be given to a patient over the phone as soon as the info is available.  On the other hand, a doctor might well want to explain the result either because a simple number or "positive/negative" isn't useful -- or because treatment options need to be discussed.