

I imagine it would be the likes of Graphene, Lineage, Calyx, and some others at the core. Probably some hardware vendors like Fairphone, Shiftphone, and probably a Xiaomi or Huawei.
Edit: ROMs maintain their own code base, but I’m pretty sure OP was talking about a larger fork of AOSP. That’s what I’ve suggested recently, anyway.
Is it offering SMS? I ported to jmp.chat recently, using their XMPP gateway for voice and SMS. They offer a VOIP option, but don’t support SMS.
I like being able to SMS, and I guess call, from my laptop. But there aren’t any Linux XMPP clients that I’m particularly happy with, so I’m just using Cheogram in Waydroid. It’s not exactly optimal.