Understanding how ZiPhone worked provides a fascinating look into the history of mobile security and the reasons why changing an IMEI is now virtually impossible (and often illegal). What is ZiPhone?

You can find this paper hosted on the Black Hat archives or the website of the Competence Center for IT Security at the University of Erlangen-Nuremberg.

Back in 2007-2008, there were legitimate reasons enthusiasts used this feature beyond theft:

ZiPhone's ability to modify cellular identifiers was tied to the specific hardware and bootloader vulnerabilities (like geohot's BL4.6 exploit) found in the earliest iPhones.

: The device will process the command and reboot automatically after a few minutes Important Limitations Modern Devices : This tool does work on the iPhone 4 or any subsequent models Legal Risk