I can tell you that you have found the right tool for building automated telephone systems. You should check out this thread:
Getting Started in TeleFlow. It contains great advice for all telephony developers, but is specific to TeleFlow/CT Developer.
We do have a product that does exactly what you are trying to do. Before you dive to far into your development, have a look at
MedicalRelay. The Appointment Reminder solution is the one that will meet your needs. Having already developed a solution, I can tell you the path your about to tread is long and rocky. It might may more sense to use ours than reinvent the wheel.
If you are interested, email sales{at}engenic.com for more information.
Regardless, I wish you good luck with your application. Welcome to the wide world of telecom development!