Well lets assume you have forgotten your security code. The master code is a 10 digit number that will always be accepted as if it were your actual security code.
You can then use the master code to change your security code back to what ever you like. When your Nokia handset asks you for the security code simply enter the master code.
How do you generate the master code?
The master code is specific to your handset and is generated using the handset 15 digit IMEI number (serial number).
Simply download the attached file onto your PC and double click it to run the program. You will see the following window appear:
Now enter your 15 digit serial / IMEI number and click "OK" (this can usualy be found on the sticker underneath the battery or by typing *#06#). Your master code will then be displayed
This program in written in Java and so you may need to download and install Java runtime.
I have not tested this extensively but I believe this will work for all DCT3 and DCT4 handste but not the BB5 range. So this will not work for the newer Nokia's such as 6630, 6680, 6280 and N-series.. etc
NOTE:
The default security code for all Nokia handsets is 12345