Almost all Nokia mobile phones have a lock code, once it is enabled, you have to enter it whenever turn your mobile phone on or change the SIM card to block access from others to your personal data and information like SMS, call log and phone book. The default code is 12345 (it may vary depending on the model of your cell phone), while this lock code is different from your service provide unlock code which is used to prevent your from using other service provider’s network.
Many people who enabled lock code usually change the default code, and some people are asking for help on the forum because they forget the new lock code they set. In order to tackle this, someone developed a security master code calculator for Nokia cell phones. You just have to enter your IMEI code (type *#06# and you get it), and it will generate the security master code, you can use this code to unlock your cell phone.
In case this calculator does not help, you may have to restore to factory settings by pressing simultaneously ‘Green’ + ‘3’ + ‘*’ and at the same time when turning your cell phone on, which is similar to type *#7370# on your cell phone.