I’m still on amber.
Calls and SMS work, as far as I know, but I’m not actively using a SIM card, only WiFi. Someone else will have to comment on the current state. I believe MMS is possible in amber with some tweaking, from what I’ve read.
Also, there is no VoLTE capability, so that’s a problem for U.S. users, and getting more critical as time passes. (Some have got VoLTE to work in Europe, I think. Not sure if with amber or byzantium.)
As for other basic functions: IMAP, WiFi, contacts import, web browsing, notifications, SSH, sound, alarms, file navigation/manipulation, web apps, music streaming, stored music playing, terminal, all work great. I believe Contacts might have some issues with dialing directly, but I think that’s being tracked already.
Firefox-ESR has the usual privacy and security add-ons that I consider critical for a safe browsing experience.
You can set a preferred DNS resolver for WiFi via Settings; for mobile, probably via Terminal.
Quite a lot of useful applications are already working with minimal or no adjustment.
Mapping, either with GNOME Maps or Pure Maps, works pretty well, and there’s also the web app option, if one wants to use something else.
Several people in the forum have got GPS/location services working, I think.
For me, the bluetooth setting is not working; I can turn it on, but it doesn’t seem to be scanning for devices. (Again, this is in amber.) Bluetooth used to work well for me, before a certain update. Hotspot didn’t work well, though.
There’s not a good, adaptive calendar app available, but there are some reminder apps that work.
I believe the online accounts function works, but I don’t use such services.
Battery life will be much shorter than what you’re used to, but it’s possible to get more idle time by limiting activities. Once suspend-to-RAM (correct term?) is implemented, standby time should improve drastically.
Some will find the weight of the device annoying. Some will dislike the thickness. I myself would like a lighter Librem 5 at some point, but don’t mind the thickness so much. Those two things are, of course, inter-related.
I can say that it has been very satisfying to see the functions improving so much in the 8 1/2 months I’ve owned mine.
And as I said, I don’t have any charging issues at all.
Edit: Oh, and the camera is not yet usable, but it’s getting there.