Comment by holowoodman

Fully agreed as a former N900 and now Fairphone+LineageOS user.

Some more things to add: On the N900 updates were quick, easy and painless to a degree that no current phone OS matches: You just to "apt update && apt upgrade", reboot will only happen when really necessary, otherwise any small component (which are just .deb packages as in Debian or Ubuntu) will just be upgraded and restarted in place, without a big download, interruption and reboot. And most importantly, without waiting for a slow vendor to collect and package up all the tiny updates into a big 1GB package that can then be delivered weeks late...

Also, Backups. The only backup solution for a non-rooted phone nowadays is "use our cloud, trust us", and even then backups are always incomplete, because an increasing number of apps set the "no-backup" flags and do (or not do) their own thing, selling you yet one more cloud subscription just to get your own data into "safety". And even with a rooted LineageOS, backups are still a huge pain and incomplete. On the N900, you could just run any old normal Linux backup software, and be done. Imagine, your phone just sending its stuff to your company tape library, no hassle!

And (didn't try this, but should have worked): remote management. SSH into your users' phones to do stuff. Run ansible/puppet/..., manage them like any old Linux box. No tedious mobile device crap management that doesn't really do most of the useful shit, only works on half the hardware and in the end is just yet another cloud lock in by some vendor.