Thunderbird's startup page asks for donations. Not saying it's a bad thing, but it's done right. How is it not enterprise and it's run by a corporation? Isn't Mozilla a corporation? Or is it not considered enterprise because it's free?
I'd call my experience with Ubuntu touch on a Oneplus 6T (pretty outdated hardware) almost minimum viable. Performance is fantastic but the app ecosystem is pretty skeletal. I'm not sure if voice calling currently works in the USA.
I use it solely as a camera, and for that it might be a tiny bit better than Android. Battery life is much better and photo quality is the same or better as far as i can tell.