Stealth SIM requires no modification of the baseband on your phone. This makes it the safest way to unlock your phone.

Modifying your Baseband invalidates your warranty. But worse still it is the most common cause of damage to iPhones. Attempts to modify the Baseband can trigger security mechanisms which can render your phone useless, commonly referred to as bricking. Moreover, even if your phone works initially, future updates from Apple could brick your phone.

read it here stealthsim