Warning: Do not enter any wrong unlock unlock codes on your Siemens C31 mobile phones. If you enter over a certain amount of wrong unlock codes on your mobile phone, your phone may get hard locked and sometimes become unusable.

1 - Switch ON your Siemens C31 with a NOT ACCEPTED SIM Card.
2 - Compose : *#0000*CODE#.

(OR)

1 - Switch ON your Siemens C31 with a NOT ACCEPTED SIM Card.
2 - Compose : *#0001*CODE#.

NOT ACCEPTED: We mean, to use a sim card from a network other than the network your Siemens C31 is locked to.
CODE: The unique unlock code for your Siemens C31.