From Wikipedia:
MeshCore is an open-source mesh networking protocol and software platform designed for off-grid, low-power text communication using LoRa (Long Range) radio technology. The system enables decentralized, multi-hop wireless messaging without reliance on cellular networks or internet infrastructure.
Use cases include emergency and disaster communications, outdoor and remote activities, [...] and experimental and educational deployments of low-power mesh networking.
[It] is designed to [...] operate in unlicensed ISM frequency bands such as 868 MHz and 915 MHz, depending on regional regulations.
The basic idea is that you get a small companion device that you pair to your cell phone via bluetooth, and via that device, you can text others or post public messages using the 915 MHz band, all without a special license.
See Scott Baker's article for more information.