 A GSM SIM card is copied by removing the SIM card and placing a device between the handset and the SIM card and allowing it to operate for a few minutes and extracting the Ki, or secret code.This is normally done with handsets that have the option of an "extended battery" by placing the normal size battery in the handset and the Ki in the now vacant extra space.This is done by allowing the device to log the interaction between the mobile telephone switching office and the handset.