23Sha-ger AtavisticPuma you're both correct. It's a very hypothetical attack vector. It's just important to know all the strengths and limits of your OS and to have a sufficiently detailed threat model to make informed decisions.
I personally am very good with not using a SIM card and always be in airplane mode, fits my threat model. I'm not worried about the 911 attack vector as something an adversary will use to harm me.
But: Knowing how it works allows me to not leave the phone around children, thinking there's absolutely nothing they could do to mess with my threat model because "I'm using GrapheneOS and it's locked".
That's why I love this forum, you'll get valuable information and people are quick to correct misunderstandings, even if they seem negligible. Helped me many times to get things right, and I'm still learning. Glad to be on the other side for once to give back to the community. :)