High Quality Low Price Prepaid Scratch Phone Calling Card/Smart Card, Prepaid Recharge Scratch Code Recharge Card with Pin

The SIM card and the switch use the authentication algorithm to calculate the authentication key and 8-digit random number at the same time. If the calculation results are the same, the SIM card will be recognized, otherwise the SIM card will be rejected and the user will not be able to make a call. The SIM card can also use encryption algorithm to encrypt the conversation voice to prevent eavesdropping.