Someone shared on Trisquel's forums a direct email communication with Purism revealing the way the company avoids being fully transparent about the fact that their device does not offer better privacy when used *as a phone* — it has privacy advantages only when the phone functionality is completely turned off, in which case the questioner claims it is nothing more than a pocket (or even stationary) PC.
Source:
https://trisquel.info/en/forum/librem5-and-why-i-am-no-longer-interested
(Score: 2) by urza9814 on Thursday March 07 2019, @12:19PM
Right, according to the response from Purism, you can't use the encrypted call features over cellular data. They say it can only be used on wifi or ethernet. Seems to be a limitation of the phone, not the network, although I can't understand what the reason would be unless it's an attempt at a security feature.