Positives--
My instinct is no longer to check my phone when I'm bored or waiting. It was rough at first, but I can be pretty content just standing in a line with my own thoughts.
Nobody can call me at any given time, whenever they want. Social anxiety has a mental toll on my energy, so not having a phone around gives a significant boost.
It's easier to accept not knowing something.
Plans are planned significantly more concretely.
Negatives--
"You don't have a phone?! What's wrong with you?!" -everybody
Not having a GPS/google makes things hard to find in certain circumstances.
There's a huge expectation when dealing with any modern service that you'll have a cell phone and can be contacted at any time. For example, it's impossible to order an Uber on a laptop.
(I realize the article is about smart->dumb, but the problems are still surprisingly similar)