Still wondering whether you should update iPhone 3GS / 3G baseband to 06.15.00? Well, if you want to unlock 05.15.04 or 05.14.02, you have to update to 06.15.00 baseband. The newly released PwnageTool 4.1.3 does this for Mac users. You can jailbreak iPhone 3GS 4.2.1 with PwnageTool as well as can update your baseband to 06.15.00 to make it unlockable. Here are some facts before you go on to update the baseband:
iPad modem firmware 06.15.00 is compatible with that of iPhone 3G and 3GS. Several of Dev Team members have confirmed that they’re running the iPad baseband on iPhone for some days now and it’s fully compatible.
If you update to baseband 06.15.00, you will NOT be able to restore to stock firmware and will have to restore to custom IPSW all the time. So continue at your own risk. If you’re confused, read the Dev Team blog.
If you rely on software unlock, your only option is to not to update to iOS 4.2.1 (if you haven’t already). If you have updated to iOS 4.2.1 and updated your baseband in the process, there’s no other option for you.
DISCLAIMER: Do this at your own risk.