Hi again! I answered your Librem Phone survey some time ago (saying it’s more a “pocket computer” than a “phone” that you’re planning for now, as you know it will be hard to provide an usual phone number for it while keeping trust in it), but I continued to think about it.
There’s something I’d be interested to buy, which hardware would be a “pocket computer” such as the one you’ve planned: a “network protector,” a trusted wifi- and/or data-connected device that I could use in ~tethering to have Internet on my computer, but that would filter hardly (but in a way configurable from the device itself) all network calls coming either from the network or from my computer.
With such a device, having a not-trusted-hardware computer would be quite less a problem, as it would be unable to make “random” network calls (the only need being to remove every integrated networking hardware, of course). That would also help maintaining usually not-connected computers.
As you’re talking about a “phone,” I’m quite sure that’s not the use you had in mind for your device. But with this function, I think it would be quite easier for you to sell wifi-only devices. Just an idea. :·)