According to Consumer Cellular, a SIM card is usually located under the battery in a cellphone. This may vary depending on model and maker. A SIM eject tool is sometimes necessary to remove the SIM card.
In some models of iPhone, such as the original and 3G versions, the SIM port is located at the top of the phone, next to the power button. The subscriber identity module is a portable memory chip that contains the phone's vital data, such as phone numbers and text records. SIM cards are necessary for phones that work on the Global System for Mobile Communications.