WooCommerce Appointments fully integrates with the Twilio SMS Notifications extension. This not only enables you to send SMS notifications when appointment status changes, but also gives you ability to remind customers before appointment takes place via SMS.
Twilio integration setup for Appointments
You can fully configure the Twilio integration inside WooCommerce > Settings > SMS tab. Appointments options are available inside a separate page, where you can configure the text notification for pretty much any case you want.