I think with the bans there was an understanding that there's no or very little redeeming value to a smart phone, so it shouldn't be used.
I think the Lubavitch attitude, based on the Rebbe's encouragement of using technology for the good, is that a smart phone can be very useful. It should be used correctly, but used.
Most yeshivas don't allow their bochurim (up to the grade corresponding to age 20) to have smart phones. There has been a strong push to parents to filter their kid's devices and their own.