> In a way we just need MQTT servers, a client with reliable push notifications and a manual key exchange mechanism. That would be really hard for govs to target.
Go even further: Meshtastic (https://meshtastic.org/). P2P E2EE texting, primarily via LoRa mesh (a mesh of long-range low-bandwidth direct radio connections) plus MQTT backup, with surprisingly nice UX even for non-techies. You can message people directly, or create encrypted groups too.
In effect, you broadcast your message (encrypted) via LoRa (travels a couple of kilometers through apartment blocks in a big city, or up to hundreds of kilometers in open countryside with line-of-sight), and then anybody else with meshtastic rebroadcasts it, up to 3 hops by default. Works OK for local chat through normal nodes, or really well if somebody within a few kilometers has a router on a roof/big hill nearby (map of opted-into-mapping public nodes: https://meshmap.net/ - IME that's about 10% of actual nodes). Optionally uses MQTT when there's any kind of internet connection available so you can chat long-range too (there's a public MQTT server available, or you can run your own) although that's not really the main use case.
No paid intermediaries or services involved, doesn't require a cell plan or internet or anything, even if the whole world collapses, you just keep on texting (for as long as you have battery).
Requires either a tiny radio gateway (e.g. https://lilygo.cc/products/t-echo-meshtastic) that you connect through with your phone via BT, or you can get a standalone device (https://lilygo.cc/products/t-deck-plus-1) but <$100 in either case. Low-bandwidth though: only text & GPS, no pictures or audio. And obviously, this is pretty deep in the weird nerd shit so it might be a hard sell for your grandparents, and by its nature it's mostly useful for the local area chat anyway. Perfect for trips to low connectivity zones though (hiking, skiing, etc).