jonwil: I use a Nokia N900.
It runs a full Linux/X11 stack with GTK and QT support.
It has the best physical keyboard of any phone ever.
I can run whatever software I want on it out of the box (no rooting or jailbreaking or anything else required).
Its one of the most open source phones in existence.
Its the best phone I have ever used and I wouldn't downgrade to an iPhone or an Android device even if someone gave me one for free (and yes I do consider both the iPhone 7 and the Galaxy S7 as a downgrade compared to my beloved N900)
I remembered the N900, amazing phone, but when I heard the news the Microsoft exec is going to be CEO (then the eventual buyout), that was the last time I bought a Nokia.