Have you heard about the GoTenna mesh project, https://gotennamesh.com/ https://gotennamesh.com/ ? I haven't got one yet, but it looks like the sort of thing yo

Have you heard about the GoTenna mesh project, https://gotennamesh.com/ https://gotennamesh.com/ ? I haven't got one yet, but it looks like the sort of thing you're describing (though its a device that works with existing smartphones, rather than being a protocol our phones could run. An advantage here is that with sufficient GoTenna mesh users in an area, one's anonymity could be increased, as typically (at least in the USA and most of western Europe) one can't buy SIM cards to access telephone networks without one's ID.