Agreed.
But I’m also unconvinced that even if they were POTM (Plain Ol’ Text Messages), the carrier would store the content. Metadata, yes; content, doubtful. And https://news.law.fordham.edu/jcfl/2016/06/02/cell-phone-forensics-powerful-tools-wielded-by-federal-investigators/ supports my belief, FWIW.
Archiving my messages without my consent is not legally substantively different from recording my calls without my consent, I suspect.