Only the correct PIN number can unlock a SIM card.
You can protect the SIM card in your cellphone even if your phone is unlocked. Unlocking your cellphone does not compromise the main settings on the phone's operating system even though the unlocking process allows it to access different wireless networks. Therefore, the process to lock the SIM card by adding a PIN code is the same whether your cellphone is locked or unlocked. A PIN code will prevent unauthorized use of your cellphone.
Instructions
IPhone
1. Tap "Settings" on the Home screen of the iPhone.
2. Tap "Phone," then tap "SIM PIN."
3. Tap the "ON/OFF" button to the right of "SIM PIN" to switch it to the "ON" position. The SIM PIN screen automatically opens.
4. Type the PIN you want to assign the SIM card in the "PIN" box, then tap "Done."
BlackBerry
5. Select the "Options" icon from the Home screen on the BlackBerry.
6. Select "Device," then choose "Advanced System Settings."
7. Select "SIM Card," then press the "Menu" key and select "Enable Security" from the list of menu options.
8. Type the SIM card PIN code in the "PIN" field, then press the "Enter" key on the keyboard.
Windows Mobile
9. Tap "Phone" from the Start screen on the Windows Mobile phone.
10. Tap "More," then tap "Call Settings."
11. Tap "SIM Security," then enter the PIN for the SIM card and tap "Enter." A message appears on the screen confirming that the PIN is enabled.
Tags: your cellphone, BlackBerry Select, Home screen, then press, Windows Mobile