Have you ever flashed a new ROM or rooted your Xiaomi phone only to find you can no longer make calls? You likely have a "null" or "invalid" IMEI. On Xiaomi devices with MediaTek (MTK) chipsets, this usually happens because the NVRAM or Secro partitions—where your Xiaomi device's 15-digit identity code is stored—have been wiped or corrupted. Common Xiaomi MTK Repair Tools

: Tools like mtkclient allow you to read, write, and wipe these critical partitions where IMEI data is stored.

It feels almost illegal. And in some jurisdictions, it is — if used maliciously.