If you're unlucky enough to lose your smartphone or have it stolen, as accidents happen to all of us, it's not only the hardware that could fall into the wrong handsets. Anyone who finds the device will also be able to access any content stored on the device, whether its contacts, music or documents. However, by implementing a SIM card PIN lock, everytime the device is powered down and subsequently switch back on again, the PIN will need to entered before the phone can be used or any of its contact accessed.
Here's how to implement a SIM card PIN on an Apple iPhone.
From the home screen, open the Settings menu
Select the option marked Phone and then choose the SIM PIN menu.
From here you will be able to turn the SIM PIN on or off or change the PIN. It's worth noting, if this is the first time you've turned the function on, you may be asked to enter the operator's default SIM card PIN. You only have three attempts to enter the pin before the SIM card is locked, after which you'll need to obtain a PUK code from your network to unlock the SIM. If you don't know the default pin, we recommend you obtain it before you attempt this. Now every time the phone is switched on, you'll be required to enter the pin before you can use the handset