PwnageTool 5.1.1 allows to create custom firmware and preserve modem version for unlock with ultrasn0w or Gevey. PwnageTool 5.1.1 supports all A4 devices:
iPhone 3GS
iPhone 4
iPad 1
iPod Touch 3G
iPod Touch 4G
Apple TV 2G
You can download RedSn0w 0.9.12b1 here and PwnageTool 5.1.1 here.
Version 0.9.10b7 of redsn0w adds a collection of useful features: It finally implements the corona-A5 jailbreak for iPhone4S and iPad2 devices still at 5.0.1. It can also re-install that jailbreak for those who accidentally uninstalled the untether. When stitching an IPSW, it can now grab your blobs directly from Cydia. It now shows a lot more info about your device (for instance, whether your iPhone3G has the vulnerable baseband boot loader, or whether your iPhone3GS has the old exploitable bootrom. (And the next new feature to be added will be built-in restore support, to provide an alternative to iTunes restores.)
Previously you needed to use Absinthe to jailbreak the iPhone 4S and iPad 2.
The iPhone Dev-Team has released RedSn0w 0.9.6b5 for unlockers stuck at the 05.14 or 05.15 basebands.
The new redsn0w 0.9.6beta5 is out. It gives both Windows and OSX users the ability to flash the iPad 06.15 baseband on iPhone3G or iPhone3GS. It fetches the baseband files directly from Apple for now (the only IPSW you ever point it at is the stock IPSW for the FW on your iPhone right now). There may be a long delay while it’s doing this (their servers are currently getting pounded).