The serial number serves to uniquely identify each device and is typically used by manufacturers to keep track of products sold, for warranty services, repairs, or to identify the device in the event of theft or loss.
A phone's serial number is usually uniquely assigned to each device during its manufacturing.
It is important to keep in mind that you should not share your device's serial number publicly, as it is sensitive information that can be used improperly.
The serial number "0123456789ABCDEF" appears to be a generic value that may appear on some devices after performing certain operations, such as a factory reset or installing a custom ROM. On discussion forums such as XDA Forums and B4X Programming Forum, several users have reported this type of situation, indicating that this serial number appeared on their devices after making changes to the phone's software or operating system.
In some cases, it is suggested that this generic serial number may appear when manufacturers do not assign a unique serial number to the device (for example very low-end Chinese manufacturers or knock-off devices), or as a result of installing certain versions of software which use this number as the default value. For devices with modified software, the serial number may change to this generic value as part of the modification process.
If this serial number appears on your device and you are concerned, one option would be to contact the phone manufacturer, seller or seek advice on specialized forums such as XDA Forums for guidance on how to restore the original serial number, if possible. However, it is important to note that changing the serial number of a device can be a technical and complicated process, and in some cases, it may not be possible to restore the original number.
