I originally did this with my wife to save money: 2 AT&T grandfathered unlimited data plans for $160 down to $15 for 2 phones on an MVNO talk+text family plan (both plans had limited minutes, but the MVNO is cheaper for add'l minutes).
We use wifi at home and at work, though since I have computers there, I don't find myself connecting on the phone that much. Also, neither of us use facebook through the app or the browser on the phone. We just use home computers or an ipad for that. That feels much safer for being physically tracked and advertised to.
So our phones have our calendar and reminders, notes, and photos, and voice and text of course (just not imessage unless on wifi). It really makes them boring and functional, and not a distraction.
The ONLY thing that we miss that is critical is maps when traveling. My wife once switched to a $40 data plan for a month, I tried to check maps with the hotel wifi so they are cached on the phone. But now we found a Garmin GPS at a yard sale for $20 and use that.