It's Not Motorola C1681 It's Motorola C168I model phone!!!
You can get the Network Unlock Pin at here Prounlocking.com and Unlock it from Network Lock,then use with any GSM Network Sim card in the Phone,You can enter the Network Pin using the instructions below:
Motorola C168i Unlocking Instructions
Warning : Do not enter any wrong unlock codes on your Motorola C168i mobile phones. If you enter over a certain amount of wrong unlock codes on your Motorola C168i mobile phone, your phone may get hard locked and sometimes become unusable.
1 - Switch ON your Motorola C168i with a NOT ACCEPTED SIM Card,
2 - Phone will display "Enter Special Code",
3 - You can now enter the Unlock Code.
NOT ACCEPTED: We mean, to use a sim card from a network other than the network your Motorola C168i is locked to.