SIM cards, or Subscriber Information Module cards, are small chips in your phone embedded with the cell phone's number and other account information. SIM cards can typically be switched between several unlocked phones.
SIM cards are located in the back of the cell phone, usually near the battery, and are about the size of a fingernail.
SIM cards are used in the U.S. but not as frequently as in Europe. Useable SIM cards must come from unlocked mobile phones so that they can be switched out.
European SIM cards are more common. Made for use in European countries, these cards are easily exchangeable, especially with a GSM-enabled phone.
If you purchased a European-only SIM card, you will need to purchase another one that is compatible with U.S. SIM card standards. International SIM cards are also available for purchase.
