Here's what we do: We always go ahead and make the next appointment, even if it's 6 months away. Two (business) days before the appointment, we send a text message. If they reply to the text, then the appointment is confirmed and noted in the AC scheduler. The day before, anyone not confirmed gets a phone call. If they don't pick up, a voicemail is left, if possible. These are noted as LM or NA on the visit reason line. Then these people are sent another text message to reply yes or no.
Of course we still get no shows. But the amount has been greatly reduced once we started to text rather just rely on the phone call. A lot of people do not check their voicemail and they may not recognize our number to call back.