1) Reduce Number of Characters in Text Template

Every 160 characters counts as a single text message, keeping your character count down will help keep the number of text messages down.  Consider updating your text templates to this single segment option:

Notification Text Template: Appt Scheduled: {{AppointmentDate/Time}} at {{CompanyName}}

Reminder Text Template: Upcoming Appt: {{CompanyName}} on {{AppointmentDate/Time}}. Click2Confirm {{ConfirmationLink}}

2) Move Important Details to the Confirmation Page 

Many text messages are longer because they include details regarding check in, parking, arrival, promotions, etc. Consider moving important details to the custom Confirmation Page located in Setup > Setup Appts & Emails > Confirmation Tab.  The Confirmation Page will appear when the confirmation link is clicked. 

3) Turn Off Automated Notifications

Although automated notifications are great, if your goal is to reduce the number of text messages, you could consider turning this feature off.  When requested, you can click the "Send Reminder Email" or "Send Reminder Text" buttons from the Appointment Detail page as needed.