I've only used linphone and set up a Grandstream ATA, I'll look into baresip too. Both VoIP providers I've tried (Telnyx and VoIP.ms) have documentation on how to set it up. Basically you get a sip username and password from them, then you log in to the sip client with that. You'll have to play around with dialing formats and caller ID settings that's where I had the most issue.
Discussion
Appreciate you mate. Im scrounging for docs and trying to figure it out.
And would i need the app on each user profile of the phone since graphene isolates each user. Plan is esim and voip numbers.
On each user you would likely have to reconnect on each instance of baresip since user data isn't preserved between user profiles. Depending on the VoIP provider, you can do this but only your most recent SIP connection will actively recieve calls, the rest you could only check voicemail or make outgoing calls.
You mentioned numbers plural, so assuming you want different VoIP numbers per user this is very much possible and as I've described above, each user has unique user data per app.