If you're looking at cloning or changing an IMEI on a specific device you would need whichever Service Suite Software applies to the specific manufacturer. For example, older generation Nokia devices could have their IMEI's re-flashed and altered through the use of a tool called "Phoenix Service Suite Software" this tool is capable of all operator modding procedures, and was meant as an internal software for engineering and programming Nokia devices. Internal manufacturer service software often gets leaked and provides the end user a high capacity of functions and manipulations that can be performed directly through its interface.