The present invention disclosed a method and system of replacing smart cards. It uses a new identification device (a new SIM) to replace an old one (an old SIM) associated with a user account. The new identification device has an identification number (ICCID). The new identification device is activated in the following manner. The old identification device communicates with an identification-management center through a communication interface (mobile telephone). And the identification-management center recognizes the old identification device. The identification number of the new identification device is sent to the identification-management center through the communication interface. The identification-management center checks the identification number. If the identification number is correct, the user account will be assigned to the new identification device by the identification-management center.