Looking back, I can't emphasize how much I loved the 3310 UI. Clean, fast, no colors, simply perfect. I'm currently using a Nokia 2600 Classic [1] with Symbian; it feels incredibly slow and cumbersome as compared to the 3310. Literally having to watch a progress bar while the phone's calculator(!) is loading.
But, that darned 2600 also refuses do die (it was already showing dead pixels, so there was some hope in the meanwhile), so I estimate being stuck with this one in the years to come also.
Another fun UI was from a Big Button Phone For Elderly People that belonged to my grandpa. I think it's a ZTE s202 [2]. Unfortunately, the microphone gave up working, so I ditched it.
That world of Old Dumb Phones is actually a lot of fun. And -- it's odd to think how much outdated-but-entirely-usable electronic waste there actually is on the planet.
Thanks, Finns, for enriching the world with the rock-solid 3310, and greetings from the other side of the gulf!
1: https://en.wikipedia.org/wiki/Nokia_2600_classic
2: https://i.hinnavaatlus.ee/p/1200/99/43/S20220must__6ee8.jpg