The iPhone dev team just released the PwnageTool 4.3 tool for the untethered jailbreak of iOS 4.3.1 firmware. PwnageTool 4.3 supports the untethered jailbreak of iOS 4.3.1 on all devices except the iPad 2. PwnageTool helps you to preserve your baseband and thus preserve the unlock on your iPhone.
They have also done with the redsn0w version for the untethered jailbreak of iOS 4.3.1. So stay tuned as we come up with the news and links!
You could download PwnageTool 4.3 from the official website of iPhone Dev Team as we are unable to post the links due to some reasons.