147: Yom Kippur is an Issur Kareis, not Missah.
And probably not. People don’t think it’s okay to text on Shabbos; they just don’t respect Shabbos. I think even teenagers still respect Yom Kippur. Those who are “frum” but only text on Shabbos probably wouldn’t on Yom Kippur, not that that made them any less of a Mechalel Shabbos.