Unlike Android, older feature-phone OSs don't support enhanced push-to-talk, voice-over-LTE, and LTE rich calling services such as video calling, but you don't yet get downloadable apps.
"Feature phones are about to be reborn. The $270 Kyocera Dura XE for AT&T looks and works just like flip phones have done for 15 years or so. It flips open, has relatively fixed functions, and no app store. But it runs on Android."