The baseband is an opaque binary blob that operates outside of the phone's main OS, and its contents are usually considered a trade secret by the manufacturer since it handles low-level hardware interactions with the main radios/etc.
Personally, I would be surprised if those systems weren't compromised by agreement. It's already common to see criminals and dissidents get busted because they think that turning a phone off stops it from reporting location data.
I'm pretty sure they have hooks into audio systems for wireless emergency alerts, but could be wrong.
In 2023 I suspect this is less and less necessary- apple silicon is very fast and a lot of voice comms goes through an app (FaceTime?) anyway but … I’m sure those capabilities are still in the baseband processor …
That’s an incredible claim to make with no source. It seems unreasonable to suspect Apple and google would allow some chips they don’t access to battery even when powered off.
Both left and right are contesting who can be more authoritarian these days.