I've had an odd problem that others in the GrapheneOS chat and I have been trying to fix. Trying to call a number results in the call immediately ending, and anyone trying to call me gets immediately redirected to voicemail. Sometimes texting will throw an error, but only when I try to send a text (receiving still works), though it currently appears to be working fine as of right now.
The fixes I tried, which were suggested from the chat, range from completely resetting connectivity settings multiple times, toggling airplane mode on and off, and getting a new SIM card. For some of the fixes, the phone would work for a while, but after a day to a few days, it would misbehave again. There is one other person on the service with an unmodified Samsung phone who hasn't had any issues.
The phone worked for a few weeks when I first got it, but after an update, this problem appeared. I've never run the phone on the default OS, I switched to GrapheneOS immediately when I got it.