Unfortunately this iOS 5.1 didn't fix battery issues and other minor bugs but an interesting thing about iOS 5.1 is that a new baseband has been introduced, bb 04.12.00.
04.11.08 Unlock - there are thousands of people are still stuck on 04.11.08 baseband and there's no solution available to unlock it right now. Without any solution to Unlock 04.11.08 baseband on iPhone 4 it's hard put a guess on iOS 5.1's baseband 04.12.00 unlock. Luckily iOS 5.1 update is still not public which means -- a lot people don't have access to iOS 5.1 update which gives us a window to warn people who are currently stuck on iOS 5's baseband 04.11.08 that Don't Update To iOS 5.1.
The Baseband 04.12.00 unlock can take more time then iOS 5 baseband 04.11.08 unlock. iPhone 4 baseband 04.11.08 unlock can take some time because it has happened before in case of baseband 4.10.01. Some iPhone 4 users who are stuck on Baseband 04.11.08 unlock have already updated their device to Apple's latest public iOS 5.0.1 update. You can jailbreak your iPhone 4 on both iOS 5.0and iOS 5.0.1 but there are still some complication in iOS 5.0.1.
For now you won't be able to downgrade to lower versions of iOS 5. If you're updating your iOS device to iOS 5.x blindly you're getting yourself in some deep trouble without even knowing because there's no way to downgrade from iOS 5.1 to iOS 5.0.
If You Already Have Updated To iOS 5.1 Baseband 4.12.00:If you're reading this with 48 hours hours of iOS 5.1 public release then there's a good chance that Apple is still signing iOS 5.0.1 which means you can downgrade your iOS 5.1 to iOS 5.0.1 and baseband 04.12.00 to baseband 04.11.08. Though there's no unlock available for both these basebands but there's still a hope that basebadn 04.11.08 will get unlocked in coming weeks but we have nothing about baseband 04.12.00 unlock. So it;s better to stay safe and where ever you are right now.
Don't Update To iOS 5.1 or you will be in deep trouble. UnlockBoot soon will post full tutorial and description, just follow UnlockBoot, Share this Post and be first who have Unlocked 04.11.08 baseband.