There was a great Defcon talk about this called The Secret Life of SIM Cards that I can recommend watching (they release the video for these some time after the

There was a great Defcon talk about this called The Secret Life of SIM Cards that I can recommend watching (they release the video for these some time after the conference). The talk itself was about a group that had an enormous camping trip (I hope that phrasing doesn't diminunise it) called Toorcamp of a few thousand people that thought it would be fun to also put together their own cell network for just them. They bought and programmed SIM cards and hid puzzles in the programs on them. But the amount of programming that can be done on the SIM card alone without involving the main processor at all was really quite fascinating and there's a lot of detail in the talk if you can track it down. Here are the slides at least https://speakerdeck.com/codebutler/the-secret-life-of-sim-cards https://speakerdeck.com/codebutler/the-secret-life-of-sim-ca...