He held his breath and pressed the final call button.
Do you have a you're trying to unlock, or would you like a list of supported network providers for a particular country? Nokia DCT4/DCT3/DCT2 Unlocking Codes by Crux Calc
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You only have a limited number of attempts (usually 5) to enter the correct code. Do not keep trying if the codes fail, as you can permanently lock the phone (Phone Restricted).
The DCT4 generation was the first to implement a challenge-response system. When you entered an incorrect unlock code too many times, the phone locked you out. To unlock it legitimately, you needed an algorithm that could generate a (also known as a Master Code or SP Code) based solely on the phone's unique IMEI number and Network Provider Code (MCC/MNC).