So many posts on this forum seem to revolve around unauthorized third-party charges that ago unnoticed for months or years, and the third party claims the victim agreed by responding to a text or filling an online survey, etc.
One thing ATT could do really easily is the first time the third party submits a charge, they could send an SMS to the subscriber from ATT itself saying "You've just subscribed to XYZ for $X.XX a month." This way if the charge is unauthorized it could be quickly detected.