"Message and data rates may apply" is the standard disclosure telling a subscriber that their carrier may charge for the texts they receive. It is a required part of every opt-in call to action.
Where it has to appear
The CTIA's Messaging Principles and Best Practices, which US carriers enforce through their registration programmes, require an opt-in call to action to disclose the programme name, the message frequency, "message and data rates may apply", and how to get help and opt out, plus a link to the privacy policy and terms. The same wording is expected in the confirmation message a subscriber receives after opting in. A 10DLC campaign submission asks for the exact call-to-action text, and a missing disclosure is a common reason for rejection.
Does it still mean anything
Most US plans include unlimited texting, so the charge rarely applies, but the disclosure is not about the likelihood; it is a consumer-protection notice that the business does not control the recipient's plan. RCS is delivered over data rather than the SMS channel, so a metered data plan could in principle be affected, which is another reason the line stays.
The rest of the opt-in
The disclosure sits alongside the consent language itself. How RCS consent works sets out what a compliant call to action contains, and the compliance checklist is the pre-launch review.