Jailbreaking provides "root" access to the Application Processor (AP), which runs iOS. It allows the modification of system files, installation of unauthorized apps, and patching of the kernel. However, it does not inherently provide control over the Baseband Processor.
When a user restores iOS via iTunes, the Baseband Firmware (BBFW) is updated. The Baseband Firmware interacts with the secure memory where the IMEI resides. While hackers have historically found vulnerabilities in the baseband firmware (e.g., ultrasn0w unlock), these exploits generally allowed for network unlocking (allowing the use of other SIM cards) rather than IMEI rewriting.
The IMEI is a 15-digit number hardcoded into your iPhone’s baseband processor (the chip responsible for cellular communication). It is not stored in the user-accessible operating system (iOS). It is stored in the Secure Enclave of the baseband firmware. change imei iphone jailbreak
When you jailbreak your iPhone, you only gain root access to the User Partition (iOS). You do not gain access to the Baseband Processor. Apple and Qualcomm/Intel have designed the iPhone so that the baseband runs its own real-time operating system (RTOS) that is cryptographically isolated from iOS.
If you want to change your IMEI for legitimate reasons (e.g., your own phone has a corrupted baseband and needs repair), a jailbreak won't help. Here are the real solutions: A jailbreak tweak that "changes" IMEI only changes
In the United States, an exemption to the Digital Millennium Copyright Act (DMCA) allows jailbreaking smartphones for the purpose of installing lawfully obtained software (interoperability). This exemption was established by the Librarian of Congress.
In the past, specifically for iPhone 4 and 4S (and to a limited extent the 5/5C), hardware devices known as "IP-Boxes" or specialized JIG programmers were used. These tools physically interfaced with the baseband chip (e.g., Qualcomm MDM6610) to rewrite the EEPROM (Electrically Erasable Programmable Read-Only Memory). installation of unauthorized apps
If you search Cydia or Sileo for "IMEI," you will find tweaks like fakeIMEI or IMEI Changer. Do not fall for this. These tweaks do not change the hardware IMEI. Instead, they intercept the AT+CGSN command (the modem command used to query the IMEI) and return a fake string to apps.
What this means:
A jailbreak tweak that "changes" IMEI only changes what the operating system thinks the IMEI is. It is visual/superficial only. It will not unlock a carrier or remove a blacklist.