you won’t
I'm not saying it's more likely that not, but I am saying I wouldn't be surprised. If you replace "one specific social media app" with "iMessage", it has already happened.
I don’t think the average American high school student has two smart phones one of which is a secret from their major source of income (their parents).
There's no use for a cellphone plan, we would just use wifi or hotspot from their main phone.