A subscriber identity module, or SIM, is present in many cellphones in the U.S., and indeed around the world. What exactly is a SIM? And what can x-rays reveal about their inner workings? We popped a SIM into our TruView Prime X-ray inspection and looked! Our x-rays revealed a simple, yet elegant IC design. A SIM is used to authenticate a user with the cellular providers service. Most SIM cards are built with traditional die packaging. In our x-ray we can see the die and the bond wires connecting it to the different component interfaces e.g. I/O and clock. The x-ray images also reveal that some of the interface modules aren’t used; this is evident in the lack of any bond wire connections.