I agree with your other responses on wifi + VOIP. But I am not a fan of the non-kyc SIMS and never recommend them. They are too easily compromised and linked by the users behaviors. Tower triangulation is permanent history. It’s logged, stored, and retroactively searchable. Even non-KYC SIMs don’t help if your social graph doxes you passively. They are a illusion of safety for people who don't really need that level of threat protection and too big a risk for those who do need it. Compartmentalization is the easier and safer route.

Which would be the VOIP options?

Yeah, I use a non-KYC SIM. However, I have not found a good VoIP app that is high quality, affordable and reliable behind a VPN to use on @GrapheneOS . As an example, I can pay roughly $100/year to mysudo on iOS and it works almost flawlessly and provides me with 9 phone numbers with unlimited calling and texting. I never have to use my physical SIM card's number with this setup for a reasonable cost. On Graphene, I would need to have a second stock device as mysudo won't let me pay them on graphene. Then I need to install google play services on my graphene phone if I want my phone to ring when someone calls/sms me. Even once jumping through these hoops, I find that behind a mullvad VPN, I don't get all incoming calls, so it simply isn't reliable enough to use a phone replacement. I have heard some people have good luck with jmp.chat instead on Graphene. I wish my legacy call needs were very limited so that could be affordable. Unfortunately, with the amount of calls I have to make, that would end up costing me over $50 USD/month to jmp + the associated data cost to someone like silent.link. And I still end up with only 1 phone number, instead of the 9 I'm getting on iOS to compartmentalize various parts of life