According to notcom, Apple has added new signature checks to 4.2.1, and an image patch will be needed to stop this baseband check. So, why’s this check so bad? You must have the latest baseband when updating your device, so the iPhone 4 baseband preservation method won’t work, because your phone won’t have the latest baseband. Therefore, any iPhone 4 owners with baseband 1.59.00 should stay where they are and not upgrade until further notice.
