Scenario 4 is for when you've got tomorrow's appointments all lined up, and now need to contact each customer to remind of the appointment, inform of the time-frame in which their tech is expected to arrive, and confirm they're going to be there.
In this case, ServiceDesk creates and sends emails to the entire set of customers on tomorrow's roster. Aside from customization as applicable to each customer, the emails look much like the following:
Here the consumer will receive the email, click the link, and (when taken to the provided interface), will either confirm that in fact she's going to be there, or (if necessary) she can reschedule for a different date (of course, if she does neither, that will be evident within ServiceDesk as well, which will spur you to resort to old-fashioned methods).
You've done the others; try this one too. Pretend you're Jane Jetson, and click on that link.