The Neo900 sandboxes the baseband, our best hope for a secure phone and last I checked they're busy arguing with PayPal to get their account back, very sad.
"We're going to address privacy concerns of non-free modem firmware by ensuring that the modem has access to no more data than absolutely necessary, so it won't be able to spy on anything that's not already available on carrier side. On Neo900 one can be sure that the modem is actually turned off when requested, not just pretending to be. Users will be notified in case of the modem wanting to do something without their consent. Unlike some other smartphones do, Neo900 won't share system RAM with the modem and system CPU will always have full control over the microphone signal sent to the modem. You can think of it as a USB dongle connected to the PC, with you in full control over the drivers, with a virtual LED to show any modem activity."
It might be possible to attack the phone from the USB connection to the baseband, https://news.ycombinator.com/item?id=12673735
Sure if you plug in random USB devices via the OTG port or the pins under the battery you could attempt this attack (if security was once again loose on those ports) but hopefully your USB keyboard/mouse/flash drive or whatever you're plugging into there is less dangerous and black-box than a baseband modem. And heck, if you are still worried nothing stops you from applying the same security measures to those interfaces as well.
and linfone or equivelent.
Just need a 3d printer so i can print the case. A bit of a brick. but a quite the "swiss army knife" of comms.
I also dont know how many people are aware just how sensitive the mic is on modern phones. I wrote a little app that turns android phones into bugs (broadcasts sound from the mic over wifi) a few years ago. It can pick up a whisper from 40m away, while when using it as a phone there is never any background noise.