The iPhone Dev Team has just updated PwnageTool to version 4.01, bringing fix for iBooks on iPhone which was problematic on pwned and hacktivated iOS devices running iOS 4.
Almost everything else remains the same except for this issue, and so it is recommended that you jailbreak your iPhone again if were having issues with the last release of PwnageTool.
Again, this PwnageTool 4.01 supports iPhone 3GS (old bootrom and already jailbroken on 3.1.2), iPhone 3G and iPod touch 2G (non MC model).
Jailbreak instructions for PwnageTool 4.01 are exactly similar to the last release i.e. PwnageTool 4.0. Simply follow the guide posted here to jailbreak your iPhone 3GS, 3G or iPod touch 2G using iOS 4 custom firmware.
Once you are done with the jailbreak, you can unlock your iPhone (on any baseband) using Ultrasn0w 0.93 guide posted here.