"Well, that should be effective, seeing as how Samsung has told all Note 7 users to power off their phones."
Clearly they would be going without any phone at all, left incommunicado forever.
I don't know why this even has to be explained. Samsung advised Note 7 owners to shut off their phones more than a week ago; even the supposedly good replacement ones that turned out to not be good. This was widely reported on TV, in print media, and on countless websites, and has been the subject of countless 'water cooler' discussions. Only cave-dwelling hermits could be unaware, and they probably don't have network coverage, so they can't receive the text. If they have turned off their phones, they won't receive the text. If they have returned their phones, the text message is superfluous. If they still have their defective phones and still haven't turned them off, they're likely too ignorant to heed the text message.