Quite often, if you purchase a mobile phone on a prepaid plan, it will be locked to that carrier.
If your mobile phone is locked to another provider, you need to contact the provider to unlock your phone. The contact numbers for the main carriers are below.

Vodafone: call 1300 650 410 or visit www.vodafone.com.au/unlock
Telstra: call 13 22 00
Optus: Call 133 937 or visit https://www.optus.com.au/prepaid/unlock-your-phone

You don’t need to contact your current provider if you are porting your mobile number to Cmobile, only if your mobile phone is locked.

Posted in: Connecting to CMOBILE