I just stumbled across a great solution. Get a mobile hotspot and put your SIM into that. Then if you need to get on the Internet while out and about, use the mobile hot spot. The mobile hotspot baseband chip can't listen to your microphone on your phone, or monitor anything else.
Discussion
I think it was Ike (I think Ike) former CTO of the CIA who was giving a talk and on video said the CIA didn't let their agents use mobile phones but fitbits were OK because they don't have a ... and then he stopped mid-sentence and said he couldn't say what he was going to say because it was classified. I'm pretty sure he would have said "baseband processor"
Baseband chip still in the phone, doesn’t require a sim for network to connect
This is true. It's how you are still able to call emergency services even if you don't have a SIM or pay for cellular telephone servicd
I was wondering about that but thought maybe not. These phones work internationally. Are all the cellular networks so compatible that this communication works without a SIM providing the details of the frequencies, passcodes, or whatever?
The baseband does not have access to the microphone. It's just the chip that handles connecion to the cell network, similar to how the wifi handles connecgions to access points.
However, the baseband can see any traffic that is unencrypted, just like the telco can. This means if you're talking over a plain old telephone service (POTS) line, the baseband can hear what is being said. However, a call to the same person over Jitsi, Matrix or a similar service would be encrypted and the contents would not be accessible to the baseband.
Your solution of using a hotspot has the advantage of separating out your telephone service from your internet connection. This means the phone number you give out to people could be a VoIP line that is not associated with your cellular service provider.
That is what it is supposed to do, but it depends how it is wired up.
"Since the software which runs on baseband processors is usually proprietary, it is impossible to perform an independent code audit. By reverse engineering some of the baseband chips, researchers have found security vulnerabilities that could be used to access and modify data on the phone remotely." https://en.wikipedia.org/wiki/Baseband_processor
the 4G/5G is integrated into the same SOC that has your CPU and GPU. this is probably why Huawei 5G tech is banned. in US most Samsung phones come with Qualcomm SOC but in other markets they use Samsung's SOC.