A splinter dev team released iBrickr for Windows and Apple OS X to jailbreak Apple iPhones with firmware 1.1.13. This jailbreak will only work on phones that have been upgraded from firmware 1.02 to 1.1.1 or 1.1.2 and then to 1.1.3. This jailbreak will NOT work on OTB (Outta The Box) 1.1.3 iPhones. As with all jailbreaks and other hacks, you could very easily end up with a nice $400 paperweight, so be very careful if you decide that you absolutely must jailbreak your iPhone.
Be warned that this jailbreak DOES NOT allow unlocking of 1.1.3 iPhones. There is currently no unlock for the 1.1.3. It’s possible that IPSF will work but so far, there hasn’t been any confirmation. If you need any unlocked iPhone stay with 1.1.1.