Just about everyone gets this wrong, including the joint that cuts my hair, so let me break this down for you.
Unless you ask me explicitly for my okay, you do not have permission to add me to your email marketing list. I’ve given you a phone number and an email solely for the purpose of communicating with me about meaningful things, and that does not include advertising. Email was bad enough; but you absolutely do not have my permission to send me a text message advertising your new text-message reminder service.
A great rule of thumb is this: If you need to communicate with me, specifically, about something connected to my business relationship with you — if, for example, you need to reschedule an appointment — then by all means contact me.
On the other hand, if you’re using an automated bulk service to send the message? It’s mostly likely garbage. Don’t waste our time.
(Confidential to the entire bulk mail industry: You realize that, every time someone does this, more and more folks block email from companies like ConstantContact and DemandForce at the server level, rendering your offering less effective, right?)