Fascinating thread. As I read the latest posts and now respond via this lovely Keychron keyboard connected to my tablet, a thought comes to mind: you speak of reporting on events in a repressive location. Simple texting via Signal is fine for a sentence or two, but are you actually seeking to support reporters? If so I might offer an alternative path to consider, as it doesn't seem this is about profit but rather supporting the free flow of journalism globally.
Typing on this keyboard is much faster & less likely to destroy my thumbs than using a phone. If detailed & accurate reports are to be prepared, even a folding keyboard would be beneficial, and can be used with a $30 tablet with NO sim card. But how to transmit securely? I would personally suggest a digital handheld radio, with an encryption performed using PGP on the tablet, and sent with a digital radio protocol. Here in the US it is ILLEGAL to send encrypted info on the amateur radio bands, but if one is sending data in a place where repression & torture are consequences of reporting, legality is not on the table. A report could be written at leisure of the author, encrypted, and then sent from a time & place where a brief burst of RF emmanates. Transmission concluded, the radio is shut down. The window of opportunity to locate & triangulate the signal is brief.
This scenario may not be useful BUT were I seeking to support journalists, this is how I would go about it. There is a little bit more of a learning curve, but in the present age I suspect this would be far less likely to be detected than monitoring cell signals. Given that a given Signal acct does have an identifier (a SIM, even if changed) and that anonymous SIM can be connected to a time/location of transmission. RF has no identifier, just the radio waves moving through the ether.