- Testing of various kinds. You can get deep inside an OSS base station, inspect and debug things, but likely may not even look at the proprietary innards of a commercial BS.
- Emergency connectivity when the backbone is broken, or did not exist. Most people would bring mobile phones anyway.
- Study / teaching, like MINIX OS or trainer aircraft which you can take apart and inspect.
- Maybe very small local cells to improve connectivity in difficult landscapes (mountains, skyscrapers, underground).