The SIM relies on a mobile modem. The modem can have secure components which purposely send other identifiers to towers, still allowing phone and SMS operation but not allowing geo-location [or A-GPS locating] anymore.

The SIM is merely embedded software so to say. Anything a SIM does could be entered in a NFC chip if telcos wanted to switch MO.

Can they prevent the SIM functioning in such devices? I doubt it unless they know in what devices you operate it and they can reverse engineer the capabilities of the modems. SIMs are pretty dumb devices and do not carry nor transmit that much data. They mostly only provide compatibility for the little data (your number, base address book, few stored SMS, and maybe some mobile wallet protocol) with the common transmission protocols.

I am not fully aware of privacy breaches telecom companies conduct

For example in the USA Trump allowed telcos to sell browsing history to companies/advertisers. I assume that also happens in many countries with less strict privacy laws than the EU. Who knows if in those countries location is sold to advertisers as well.

Not necessarily a “breach” but it does make the user the product, more often than not unknowingly even. Definitely not an example of privacy.

I am 99.999...8% confident that in many authoritarian nations law agencies have real-time access to SMS. We know from the NSA files that anything not encrypted they track. Even that they can turn on camera/mic remotely.

Facebook even applied for a patent for turning on mic remotely, some years after Snowden revealed everything. Zuckerberg himself has long covered his laptop’s mic/camera with duct tape. Pictures of that go back to last decade.

With device based encryption, only encrypted apps, hardware selected to be secure against specific man-in-the-middle attacks, black doors, and leakages the AnoPhone may be one of the most secure options available.

Of course, biggest threat to security is still the user. Don’t renew the VPN after first year and install an email client which works with gmail... good luck if you relied on the security of the AnoPhone.