[tptacek]

You've given up the argument at this point. If you don't trust your phone's manufacturer not to backdoor their own chips, the baseband doesn't matter. If you're concerned about the Qualcomm baseband chips in an iPhone, you're talking about what is probably (depending on your phone) just a USB peripheral.

The baseband parts here are not, as message board C.W. would have it, top secret unknowable wizard hardware. You can get the part numbers and look them up.

There's a lot of weird mythology about these modem parts. The thread you linked to included someone claiming that basebands were DMA'ing into host memory --- you couldn't even do DMA over the HSIC USB the parts were using. Like, it wasn't even physically possible.

(I have no idea what a 5G Snapdragon Xwhatever can do today, but I assure you that Apple's security team does).