If you wish to stop receiving SMS marketing messages, please send an 'opt-out' request to the company involved.
That'd be right - yet more profit for them!
Cos they're never just a regular number that you can send a text to within your monthly bundle, they're always at premium rate.
Nice "work" if you can get it!
I'm also reluctant to respond in any way, shape or form to the SMS marketing messages, as, like spam emails, responding (even to opt out) confirms that the number/email is a valid & active one!