Nokia 2600 - Manual (Page 13)

enter the PIN or PIN2 code incorrectly three times in
succession, you are asked for the PUK or PUK2 code. If you
do not have them, contact your service provider.
The module PIN is required to access the information in the
security module of your SIM card. The signing PIN may be
required for the digital signature. The barring password is
required when using the call barring service.
To set how your phone uses the access codes and security
settings, select Menu > Settings > Security.
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