Warning !!!! If you have a Jailbroken and Unlocked iphone, Stay away from this upgrade. If your on 4.0, Stay there untill a new unlock comes out.
Use TinyUmbrella to save your blobs on Cydia, just in case you need to use them to roll back, or use them for the jailbreak and unlock process.
Apple today has released iOS 4.0.1 in a bid to fix the reception issue which has been plaguing iPhone 4 users since its launch last month. This new update addresses the reception issue which is experienced which the phone is tightly griped in the left hand.
iOS 4.0.1 is fully supported on iPhone 4 and iPhone 3GS. iPhone 3G is also supported but the users are officially unable to do multitasking and wallpapers unless you know where to look for it. An iPad version of iOS 4 is also expected to be released by fall 2010.
To update to iOS 4.0.1 for iPhone, all you need to do is to connect your iPhone with your computer via USB and start iTunes. You should now see a message as shown below. Simply click on “Download and Install” button to get on to the new iOS 4.0.1 firmware.
Note: Except for iPhone 4, all iPhone jailbreakers and unlockers are highly recommended to stay away from this release. This release contains new baseband 05.13.05 which will not work with ultrasn0w 0.93. If you rely on an unlock and updated to this firmware now, you will lose your unlock for God knows how long. You have been warned!
Download Links for iOS 4.0.1 (Official from Apple)