Here's something wild from recent (but not yet published) study reported at Neuromarketing:
Including the recipient's first name in a reminder text message for medical appointments cut no-shows by 57%.
Here's the wilder part:
There was no impact when they used the patient's full name ("Robert Jones") or last name with title ("Mr. Jones").
It was first name only that made the difference.
That might work for you. Test it! Not only in text messages, but email and even direct mail.