What? Why? How? Answers to these questions, AND MORE, in this ultimate jailbreaking guide for iPhones, iPods and iPads.
Jailbreaking is...
...freedom for iOS users, giving them a way to break free from Apple's restrictive App Store ecosystem, install whatever software they want, and use their phones however they please. Technically, each jailbreak is a hack; an exploitation of some flaw in the devices' operating systems, used to install unauthorized software. This software generally includes some kind of alternative App Store, called either Cydia or Rock.
Jailbreaking is openly discouraged by Apple, who updates various jailbreak exploits out of existence as fast as hackers can find them, but even after three years of pressure from Jobs and Co., the jailbreak scene is still as lively as ever.
...and worth trying because...
...the jailbreak app stores are packed full of previously forbidden goodness. This ranges from replacement text message apps and device skins to Wi-Fi tethering apps and access to hidden device settings. The best case to be made for jailbreaking is a showcase of the apps it lets you download.
Gizmodo has all of the details and techniques HERE!