I've been noticing this problem over the last few months. I receive verification code/security code texts from some sites but most of them I don't. At first I thought it was a problem with one of two sites but it keeps happening. I do get them sometimes. Am I missing something in Settings or could it be on AT&T's end? For one site I was just trying, I was on my iMac first and then tried on my iPhone. I didn't receive anything.