PIN code: PIN code can prevent others from using your SIM card without authorization. When you load the SIM card for the first time and start the device, you will be asked to enter the password. The code is 4 to 8 digits long and is usually provided with your SIM card. However, it is recommended that you change the original PIN to your own PIN. Instructions on how to change the PIN code are provided in the user manual or Nokia website. UPIN code is usually provided with USIM card. The USIM card is an enhanced version of the SIM card of UMTS mobile phone. The length of PIN2 code is also 4-8 digits, which is attached to some SIM cards and needs to be input when accessing some services. If you enter the wrong PIN code three times in a row, you need to use the corresponding PUK code to unlock it. Read more about PUK code below. PUK code (personal unlocking code): the length of the PUK code is 8 digits, and you need to enter the PUK code when replacing the lock PIN code. When changing the locked UPIN code, you need to enter the UPUK code. When changing the locked PIN2 code, you need to enter the PUK2 code. PUK codes can also be provided by your network operator or service provider. Password protection/lock code: Password protection or lock code can prevent others from using your device without authorization. The default code provided by the device is 12345. However, it is recommended that you change the default code to your own value. For instructions on how to change the security code, please refer to the user manual or visit the Nokia website. Please store the new security code in a safe place, not with your equipment. If you receive an error notification after entering an incorrect security code for three consecutive times, please restart the device and wait 15 minutes, and then try again. If the problem persists, please contact your operator or your local Nokia customer service network. Restriction code/password: When using some network services (such as call restriction service), you may need to enter a restriction code or password. Please note that not all network operators support such services. When you insert a new SIM card, if the device displays "Enter restriction code", it means that your device has been locked to use the network of one operator and cannot accept SIM cards from other operators. Please ask your network operator or service provider for help. Other PIN codes: When accessing the information in the SIM card security module, you need to enter the module PIN code. When signing a digital signature, you may need to enter a signature PIN code. Important instructions!