Step 3. Disable the SIM card

Before you use an app to try and track your device, the first thing you should do when your iPhone goes missing is call AT&T or Verizon and ask the operator to deactivate the device's SIM card. That way, the thief who stole your phone will not be able to purchase apps or place phone calls with your device. The option, unfortunately, does not block the person from accessing all of your data and settings, but you can always use the AutoLock Wipe feature to take care of that.