I've also read that some FT-17 tanks were dug in during the Winter War to serve as MG pillboxes
Yeah, they never saw any combat though, and were left where they were after Winter War ended. The Soviets then dug them up and took a few photos. Dunno what happened to them afterwards, but I'd assume they were scrapped.
Here's a photo posted in the Captured vehicles- thread.
I believe dug-in T-26s or just their turrets were used in one of the defensive lines built during the Continuation war, but I don't know which one. Probably Salpa-line.