You must activate Lock SIM card before you can change your SIM PIN code.
How Do I Lock My Sim Card In My AT&T Samsung DoubleTime™ (SGH-i857) Mobile Device?
How to lock your SIM card and change your SIM PIN.
SIM Card Lock
Prevent another user from using your SIM card to make unauthorized calls or from accessing information stored on your SIM card by protecting the information using a PIN code.
When enabled, your phone will ask for a PIN number each time you use the phone. Using this option you can also change your SIM PIN number.
- From the Home screen, touch Applications > Settings > Location and security.
- Touch Set up SIM card lock.
- Touch Lock SIM card, enter your SIM PIN code, then touch OK.
Change SIM PIN
- Touch Change SIM PIN
- Enter your old SIM PIN code and touch OK.
- Enter your new SIM PIN code and touch OK.
- Re-type your new SIM PIN code and touch OK.
Thank you for your feedback!