Hardwired software or functionality imposed by companies or authorities

[diodelass]

The idea, going back to the failed Neo900 project includes hardware switches on the modem and radios as well as a hacker-interface allowing a future receive-only POCSAG pager receiver module which allows you to be passively 'online' especially if you can redirect incoming calls to your regional commercial(or amateur radio, or low power local) paging service where you receive a 'text message' via POCSAG service that you can call back immediately or whenever you feel safe to power up your telephony modem or VOIP modem.
Back to the thread above, we need a good low power receiver IC to build a reference dev kit so the software devs can integrate stealthy operation into the OS.

I've been doing something like this for nearly 30 years, though not quite the way you describe. My provider has a feature where when someone leaves a voice message an external device (receive-only pager) is notified. This is a legacy feature from the days when range was limited, there were lots of areas without service, and airtime and roaming charges were expensive. (In those days many times one would return the call via land line or pay phone rather than firing up the cell phone.)

This feature still works. So what I do is leave my phone off with the battery removed most of the time and just leave the pager on. When I receive notification that someone has left a message I can choose the time and place for checking it and responding.

Pagers have lots of privacy issues of their own. POCSAG (and FLEX) seem to be used mainly to transmit clear text that just anyone can receive with a $25 RTL-SDR and multimon-ng. There are a lot of pager networks here that I've seen for myself which are used by hospitals, and they're constantly transmitting sensitive and personally-identified medical information in clear text. It's really not good.

With that being said, a Pinephone with built-in pager functionality could easily be close at hand. All it would take is an RTL-SDR module, which the Pinetab already has as an option, and then the demodulation could be handled in software. It might not be energy-efficient, but there could be ways around that too, or maybe a more appropriate specialized pager-receiver module. The antenna sizes required are perfectly practical, at any rate - generally UHF, in the same neighborhood as cellular.