When sending customers advertising through text messages, must you give the customer the option to opt in/out?

Pulled from a quick Google search: In February 2011, the Federal Communications Commission (FCC) announced a significant telemarketing rule change affecting text message advertising. The new FCC “robocall” and text message advertising laws make it illegal for telemarketers to place calls or send automated texts without express written consent from the consumer. Additionally, consumers must always be given an opportunity to opt-out, even after he or she has opted-in.

Thank you!!