This version provides true carrier unlocking for iPhone OS 3.1.2 and baseband 05.11.07 by taking advantage of at+xemm crash exploit discovered by ih8sn0w.
The Blackra1n jailbreak process installs a new app--called Sn0w--onto an iPhone. It unlocks your iPhone, making it usable on any GSM carrier network. More information about the jailbreak can be found on GeoHot's blog.
Please note that by jailbreaking an iPhone, you may be violating your terms of service and voiding your warranty. CNET does not recommend jailbreaking; proceed at your own risk.