"In sociology, a tipping point is a point in time when a group—or many group members—rapidly and dramatically changes its behavior by widely adopting a previously rare practice." [1]

Do we need 10% of population to stubbornly use dumb phones, and then, voila. :)

"Scientists at Rensselaer Polytechnic Institute have found that when just 10% of the population holds an unshakable belief, their belief will always be adopted by the majority of people who simply change their beliefs if their last two social interactions agreed with a new one." [ibid]

1: https://en.wikipedia.org/wiki/Tipping_point_(sociology)