I receive sms messages from both a taxi service(on way/arrived) I use and a physiotherapy clinic(reminder that you have an appointment tomorrow at ...) that I use. I find these useful and am grateful to receive them. On the other hand if they were automated voice calls I would hate them with a passion, I just can't describe how much I hate being called by an automatic service. SMS seems like the right way to go. Given that you do that I think you have a valuable service that I would be happy to use.

It is possibly a company local to me (SLC, UT) called Smile Reminder, or at least one of their competitors (http://www.smilereminder.com/)

I built the same thing 8 years ago but it did the opposite of what patio is doing... it called/texted/emailed the dentist (or dentist's secretary) and told them to call their customer.

As someone else mentioned, his monthly enterprise account seems priced too high. You can buy full practice management software for this much.

His blog post points out that the price is on purpose to dissuade healthcare customers. Not sure if that's the best idea, but it explains his pricing.

My parish does the same thing with something called "Callpost", but it's outbound-only; there's no schedule component.