On the Nokia website, click on Support and enter the model number, 3120, in the block on the upper right of the screen. Click on the photo of a 3120 phone and click on the User Guide. Scroll down to the security settings.
On your phone, click on Menu, then Settings and then Security Settings. Click on PIN Code Request and follow the prompts. It requires the SIM code to entered every time the phone is turned on. Some SIM cards do not allow the PIN code request to be turned off.
Under the Security Settings, select Call Barring Service and select what you want to block, such as incoming calls, international calls or outgoing calls. Get a call barring password from the phone's network service provider to activate the service. The network service provider can also help set up a user group that specifies incoming and outgoing calls to a list of phone numbers.
Under the phone's Security Settings, click on Access Codes to reset the security code, the SIM code, the SIM2 code and the barring code. The preset security code on a 3120 phone is 12345. Read the Nokia User Guide for the 3120 phone for additional guidance; expert help is also available from your network service provider or one of its retail outlets.