AriX and Ben have announced the immediate availability of iJailBreak 0.5.1, the latest version of the open source Mac OS X jailbreaking utility. iJailBreak 0.5.1 allows iPhone (and soon iPod Touch) users the ability to jailbreak, and if so desired, unlock and “hactivate,” their device in mere minutes. Currently iJailBreak 0.5.1 is an Intel-architecture only application that supports Mac OS X Tiger and Leopard.

This process also works for other firmware versions, however iJailBreak 0.5.x was written with 1.1.3 in mind, thus it’s suggested that you only use iJailBreak 0.5.x for 1.1.3. Note that the unlock only works for iPhones with Boot Loader 4.6 (all iPhones that came pre-loaded with 1.1.2 or 1.1.3 have Boot Loader 4.6).

iJailBreak 0.5.x fixes many of the issues found with the “1.1.3 Soft Upgrade"-based method, including the inability to play some DRMed music. Those who have used the 1.1.3 Soft Upgrade include users of iJailBreak 0.4.x and iJailBreakMobile 1.0.

read it here ijailbreak.com