Android unlock methods compared
Android is not one platform when it comes to unlocking. Each manufacturer implements SIM locking differently, so the right method depends on the brand, model and region.
Network code (NCK)
Used by Samsung, Motorola, Nokia, Alcatel and many others. A code is generated from the IMEI and entered once when a foreign SIM is inserted. Simple, permanent and reversible only by the operator.
Remote / server unlock
Used by Google Pixel, newer Xiaomi and most devices sold in North America. The operator updates a record against the IMEI and the phone applies the change the next time it connects.
What to avoid
Avoid unofficial software flashing, modified firmware and 'free unlock' apps. They can void the warranty, break VoLTE and banking apps, and in many cases relock after the next system update.
A legitimate IMEI-based unlock never requires root access or a custom ROM.
