I do recognise that a lot of it is probably just playing up for the joke, but I assume it has to come from somewhere. I regularly see posts where basically Person A sends an odd image/message, then follows up with “wrong number, sorry” and Person B responds with “wait stay”.
Do Americans, as a rule, not save phone numbers? Or is it purely a bit that has become a trope?
I don’t think this happens much in real life, I would assume most people use contacts. Though it is a commonly used format for fake text messages meant as memes.