Just stumbled over this e-ink based mini smartphone
www.nttdocomo.co.jp/product/feature_phone/ky01l/ (use Google Translate to render Japanese to English)
Here is an English language article:
www.fastcompany.com/90254953/kyoceras-new-business-card-sized-phone-is-the-thinnest-ever
A short demo video is at
youtube.com/watch?v=hX7GoymPSJM
A pity it is so small.