First device I used to read ebooks was running PalmOS, a Tungsten T, I think?
Later I bought the "
100 Classic Book Collection" cartridge for the Nintendo DS and quite enjoyed that even though it was far from ideal as an electronic book device.
I eventually discovered the wonderful world of dedicated e-readers and bought the Kobo Touch, later replaced by a Kobo Aura, and now I'm using a Kobo Clara HD.