What happens to incoming texts if SMS is disabled?

I am reading through the TCR requirements for SMS and see that without registration, SMS will be disabled. Honestly, I am not doing ANY outbound SMS with RC, as I only have it on to catch texts from customers who text the wrong number (having it sent to email and I respond with my regular cell text). So my feeling is to skip the TCR and let the SMS be disabled. But I would like to know what outside folks would see if they try to text my RC number AFTER SMS is disabled. Do they get the "this is a landline" notice, or do they just get nothing and not know that I didn't see it? ANy help would be appreciated. Thank you!