The subscriber identity module card is a 128-kilobyte microchip used to store the service books and mobile service authentication information for GSM, or global systems mobile communications, phones sold by cellular carriers such as AT&T, Verizon and T-Mobile. SIM cards are also capable of storing text messages, contact names and phone numbers for backup or to transfer between phones. In order to use the SIM card for these purposes, you will need to get an activated card from your cellular carrier, insert it into your cell phone and copy your contacts to the card. Tips Warnings Writer Bio
