Love the dedication to privacy but I'm curious why not just buy a prepaid SIM with cash? Can use that in any phone and it's not "hacky" so won't cause compatibility issues etc.
I use GrapheneOS with a prepaid SIM myself and it's great.
No longer using a traditional phone carrier. I bought a used phone with cash and did the rest paying with Bitcoin. I've set up my new phone to work by using CalyxOS, a silent. link eSIM, and the XMPP protocol. The instructions I used to use XMPP (via JMP. chat & Cheogram) are here:
https://www.makeuseof.com/replace-your-carrier-on-android-with-cheogram-and-xmpp/
I'm sure there will be lots of headaches, but so far I've been able to use it as a daily driver and spend less than I did with my old phone plan.
Discussion
Good question, I used a SIM from Mint Mobile last year and it worked great. Just wanted to give silent. link a try
Got me curious now might have to check it out myself
You're always on Roaming (or WiFi) with Silent, and you don't use the number they give you, but a VOIP instead. It's way different. There's a Citadel Dispatch episode on it if you're curious.