Nkrs
After two months of having an ordinary dumb phone, I often forget that I have a cellphone at all. I listen music on it (for about 6 hours daily when it's a working day and I'm not at home), make calls and send texts, and even take a picture occasionally. The battery needs to be charged once every 11 or 12 days, which is significantly longer compared to the old phone which had to be charged once (or even twice) per day.
Martijn
My Nokia 206 (a predecessor to @nkrs' phone) had both a Facebook app and WhatsApp app build in. And I could use Opera Mini for most other things (including Sublevel). I do not recall if Facebook offered an app for Messenger, but it would be worth looking into. Using a feature phone does not mean you have to cut off communication channels you are currently using.
Nkrs
At uni, we used emails and Google Talk on the PC along with text messages over the phone, and then Facebook and it's messaging service once smartphones became popular and more convenient. At that point I believe I was in the same situation as you - all my communications with other people at school were on Facebook. Nowadays they use WhatsApp or Viber or whatever else there are cheap data packages for; I really don't have the means and the want to catch up.