Note that 3G is still current-ish around the world, and is often what you'll pick up in rural areas many places. In my country, it's pretty much just major city centres that have 4G, and many phones still exist which don't support it. In my city, it's often incredibly difficult to pick up 4G because of granite buildings.

Osmocom's goal is to create an open source implementation of mobile telecom standards. An open source implementation would allow people and companies to build non-encumbered mobile devices and telecom networks. This is important if you think free software is generally an important thing.

Osmocom run a GSM network at CCC each year, allowing people to place calls and send text messages to each other for free.