There are two cases in which we would lock device. First, if you report your phone as lost or stolen through My Account, we will lock the device to protect your personal data. The claims process for lost and stolen devices states clearly that the device will be locked if you proceed.
Second, your device will lock if we cannot charge your payment card and you fall behind on payments. In this case, you would have received a number of notices via email and messages on the device screen informing you that the device will lock if the due payments are not made. Return the device as advised via email and update your payment details, otherwise your credit score will be affected.
A locked device can still be used to make and receive emergency calls, modify cellular data options (on/off), flight mode (on/off) and Wi-Fi settings, and view the IMEI of the device, but cannot be unlocked. Once the device is locked, you will not be able to access any data or content stored on the device.