An automated SMS system can be setup that will automatically retrieve appointments from your database, send the reminders, and provide a report on those without Mobile phone details so they can be reminded by a phone call. This can all be done over the Internet - no need for a Mobile phone at your location or for staff to key in the messages. Typical savings are around 50% on call costs, and several hours per week in staff labour. Let's face it - confirming patient appointments isn't really an exciting job and your staff could be better put to use elsewhere.
Even if you don't want to do this immediately, I suggest you start taking patient's Mobile phone details (and email addresses) so that you don't limit your options in the future.