iPhoneSimFree claims to have a working version of their software SIM unlocking application for iPhone 1.1.1. They credit the iPhone Dev Team for finding a method for "jailbreaking" the 1.1.1 filesystem. The side effect is that they are now able to load their SIMFREE software onto the iPhone.
Our sincere congratulations, to the iPhone/ iTouch Dev Team for their brilliant work in finding an ingenious way to jailbreak the 1.1.1 system. This exciting news means we are now able to gladly welcome all SIMFREE unlocked phone owners to UPGRADE to 1.1.1 if they so wish
They also offer instructions on how to debrick unlocked iPhones that were prematurely upgraded to firmware 1.1.1.
iPhoneSimFree's solutions are commercial and require purchase through one of their resellers.