We use AC Reminders. We have it set to call the patient at the home number several days in advance and to text them either 48 or 36 hours in advance. Or, if the appointment is put in for the next day they get one within 10 minutes of booking the appointment. If they are set up with email, they get one the day it is booked, even if the appointment is months in advance. We don't have to call anyone to confirm appointments anymore, unless they don't respond to the automated system. If they do confirm via phone or text, it pushes the confirmation to the schedule and makes their name BOLD, so I know they got the message and are confirming.
It has saved me countless hours of trying to reach people. We've been using it for almost 2 years, I think.