Sim Cards store information and are used in GSM cell phones. GSM stands for Global System for Mobile Communications. Sim stands for Subscriber Indentity Module. The Sim card stores your phone number which enables you to swap your sim card to another gsm wireless phone and use it as long as the other phone is on the same carrier. If the other cell phone is not on the same carrier than your phone needs to be unlocked. If your phone is locked you will need to ask the carrier to unlock the phone. Or, you may find information online on how to unlock the phone yourself.

Sim cards can also store phone numbers and contacts. Also, when traveling you can purchase pre-paid sim cards which will have a local number.

There are sim cards for many mobile phones and also what are called blank sim cards, international sim cards and pre-paid sim cards.   T-Mobile Sim Cards, Vodafone Sim Cards, Virgin Mobile Sim Cards, Orange Sim Cards, 02 Sim Cards, 3 Pay 3 Network sim cards, Mobile World Sim Cards, Lebara Sim Cards, Nomi Sim Cards, Pay as You Go Sim Cards, UK Sim Cards, Dial Abroad Sim Cards.   There are sim cards for 2G and 3G cell phones.