The primary advantage of PwnageTool is that it is able to remove baseband upgrades from firmware updates so that one can upgrade without losing the ability to unlock. For instance, you could use PwnageTool to create a custom 3.1.3 firmware without the 5.12.01 baseband upgrade which would make your phone incapable of unlock via blacksn0w.
I guess the process will be clearer when I use this, since I didn't realize you could make a 3.1.3 that didn't have the new baseband.
Another benefit is that this method can patch changes made to the firmware by Apple which close exploits. This means that once your phone has been jailbroken, it can always be jailbroken. There is nothing that Apple can do to firmware 4.0, for instance, that would make it impossible to jailbreak using PwnageTool
even if phones already updated to 4.0 or that came with 3.1.3 could not be jailbroken.
This was confusing. Are you saying I can make a 4.0 for the 3G that doesn't have the newer baseband? I thought you had to wait for the Dev Team to jailbreak at a new OS?
For owners of 3GS iPhones, custom firmwares also have the advantage of being installable even if Apple is no longer signing that version of the firmware. This is because the initial jailbreak patches the signature check out of iBoot. A 3GS owner can no longer restore to the official 3.1.2 unless he has his SHSH on file, for instance; if he is jailbroken, however, he can always restore to a custom 3.1.2 firmware.
Since your phone is a 3G and you probably have already upgraded your baseband to 5.11.07, and since you do not want to upgrade to 3.1.3, the primary benefit of PwnageTool for you is that it is a one-step solution. Once you have created your custom firmware, you will be able to restore to it any number of times without needing to re-jailbreak your phone.
It's not that I didn't want to upgrade to 3.1.3; it's that 3.1.3 would remove my unlock capability. You're saying it won't? Just when I thought I understood all this, I'm confused.
It all comes down to personal choice, especially for a 3G owner. There is nothing wrong with using Redsn0w, and it is certainly easier for a beginner.
If you decide to use PwnageTool, as an AT&T subscriber you should be sure to use Expert Mode and *uncheck* the box for activation.