This is clearly written by an adult who forgot how most children behave. If they're the only ones without a smartphone, they'll be single out. Especially with how prevalent online communication has become. They might not be bullied (though they probably will be), but growing up as the outsider comes with is own can of worms. They'll most likely survive it, but it'll have it's effect... But everything has consequences…
I think your take is valid, but also missing large areas. Even if they AREN'T bullied for lack, they'll miss out on all the socialization. When I was a teen people talked on the phone, they hung out at the mall. I barely did. When not at school, I stayed at home to care for my younger brother and make sure dinner was made (child of a working single mom). I went out of state to my dad's place every summer, so I never…
you can have a smartphone (I don't) and be very miserable and lonely (i’m not). I bet that's even the daily experience of a lot teenagers.
A smartphone may help to get in contact with people, but it's not a necessity by a far stretch.
Again: a (sometimes painful) emotional and social education is what teenagers need. Soft skills are hard to learn.