A SIM card (Subscriber Identity Module) is a rectangular memory chip used in some cellular telephones. It holds personal identity information such as: cell phone number, phone book, text messages, and other data. The SIM card makes it easy to hold this data and activates the phone. Most cell phones come with built-in memory and the SIM card which can be thought of a memory card; stores limited information.
A SIM card is very helpful. If for some reason your phone is not working, you can slide it out of your phone and into another. You cell phone carrier will bill you for the call even though you used another phone. The same is possible if you upgrade your cell phone.
To use a phone that accepts your SIM card, the other phone must be from the same carrier or unlocked. Some phones are locked by carriers so that SIM cards only used by that carrier can be used in the phones they make. If you’re traveling across the country or over seas, (if your headset is not locked) you can buy a SIM card that will allow you to talk at minimal cost to. For example you can purchase a prepaid SIM card or SIM cards made by overseas carriers.
