On the software side the base stations all run the Osmocom (Open Source Mobile Communications ... on the network. Everyone at Electromagnetic Field 2018 gets one of these GSM phone badges.

Different mobile phone networks around the world use different bands. A phone can only be used on a network if it supports the correct band(s). Quad-band usually refers to a phone using GSM ...

There are legitimate privacy and legal concerns, but there’s also some fun tech in mobile cell-phone stations ... tapping/intercepting unencrypted GSM signals. It’s great if you want to ...