Many forum moderators enforce strict rules against IMEI changing for stolen phones. Legitimate use (repairing a lost IMEI after a corrupted flash) is supported. Unethical use leads to bans from the forum and blacklisting of the dongle's serial number.
Many newer phones require entering "Download Mode" or "EDL Mode" via specific test points—tiny conductors on the motherboard. Forums host thousands of high-resolution diagrams and video tutorials for finding these points without damaging the device. nck pro dongle gsm forum