Apple always takes measures to make it difficult for hackers and jailbreaking community to jailbreak and unlock iPhones. The new version of iOS available is iOS 4.2.1 and ever since its release, jailbreaking community and hackers were working towards jailbreak and unlock apps. To make it even more difficult for iPhone users to use jailbreak and unlock apps, Apple has added a new baseband requirement for iOS 4.2.1.
Now that untethered jailbreak for iOS 4.2.1 available with GreenPois0n and RedSn0w, you may be interested in using the tool for untethered jailbreak. However, if your iPhone is already unlocked or you plan to unlock your iPhone after using the jailbreak tool, you should stop for a minute before upgrading your iPhone 4 to iOS 4.2.1 because there is a catch.
Firmware Umbrella is usually suggested to upgrade iPhone 4 to iOS 4.2.1 without upgrading baseband. However, some users complain that there is a problem with respect to Umbrella because the software gets stuck in recovery mode. iTunes throws an error, but many users have said that even though there was an error it works fine.
MucleNerd has said that his iOS 4.2.1 is working fine and that Umbrella way may be prevented by Apple. Using jailbreaking tool with iOS 4.2.1 with upgraded firmware is not a problem, but if you want to unlock, you can’t do so because new baseband of iOS 4.2.1 doesn’t have any unlocking tool as of now.
The suggestion from Umbrella team is that you should restore to iOS 4.1 again and stick to tethered jailbreak. You need iOS 4.2.1 only if you urgently need untethered jailbreak. If you have an unlocked iPhone, using Umbrella at this point to upgrade and jailbreak is too risky. It is better to stick with 4.1 as of now and wait for a new unlocking tool to be made available for unlocking new baseband.
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