I used a Kyocera DuraXE for a bit while travelling. It's rugged, and supports LTE/tethering, but I abandoned that experiment due to how unpleasant I find T9 texting. I was recently looking for a new phone for my father... he currently uses a Gingerbread-era LG slider phone with keyboard. He's never connected it to data or wifi, only uses it for calls and texting. Doesn't look like there's much available to serve his…
I used this phone until the end of 2017, at which point the outdated browser and dead app store (free apps only) started to seriously limit its functionality, but if you don't need those it would work just fine. I use a KeyOne now, but I miss the Classic's smaller form factor.