The Pwnage Tool by the DevTeam hacker group allows you to create custom iPhone firmwares for the purpose of jailbreaking, to get full control over your device (see why you should jailbreak here).
Currently, the Pwnage Tool version 4.1.2 allows you to jailbreak a device already on the latest firmware. However, it will NOT unlock the device, enabling it to be used with different GSM carriers worldwide.
You can also use greenpois0n by Chronic Dev to achieve the same. There’s practically no difference between the different tools, except for the fact that they come from different dev teams.
