Bought one yesterday, I have to say that KaiOS is still veeeery immature, so far very far behind series 40/60 nokias. If you can find a Nokia 208 or 515 which are the last they made with 3G+ you might be better off.
Phone game apps are the most addictive but if you never download them you won't get into it. Games have 4 caracteristics that makes them addictive: winnable, it has goals, novel challenge that keep you in state of flow, feedback. These things could also be used in reading books and that becomes addictive in a good way.
Tl;Dr phone apps are the best thing to aquaire skills in the future. If you block or hide notification and not download addictive apps you will be fine.
In that case, why not communicate via Twitter or the Blockchain (tm)? Do you post pictures of yourself naked on Instagram as well?
Every person and every company has significant secrets.
I can also easily take my smartphone with me when I think there is a real need. The 4g dumbphone can share the internet to my smartphone.
I had a dumb phone for a year or so until maybe half a year ago. The ways I found to waste my time without smartphone were refreshingly different. Most importantly, thinking and wandering in my own mind without the urgent need to check every new thought from the internet. Long story short, there is now nokia 8110 with 4G and wifi available, I am likely going to get one of those soon and turn my smartphone off until I really need it.