Apple iOS 6.0 firmware which was released earlier yesterday also brought some new baseband for iDevices. iOS 6 brings new baseband 3.0.04 for iPhone 4S, baseband 4.12.02 iPhone 4 and iPhone 3GS Baseband 5.16.07.
Many iPhone users who rely on unlock may have stuck on these baseband by upgrading iOS firmware to iOS 6.0. Now the question is that is there any possibilities to downgrade your iPhone iOS 6.0 baseband to other unlockable baseband. See detailed answer after the break.
If you have a 3GS (made before week 28 of 2011), it’s possible, but it involves some steps which I will write-up soon.
If you have an iPhone 4, it’s not possible, unless if the iOS is still being signed by Apple. For instance, if you have already installed iOS 6 on iPhone 4 that has baseband 4.12.02, you can downgrade to iOS 5.1.1 which has baseband 4.12.01, for as long as iOS 5.1.1 is still being signed by Apple. Apple will close the signing window within 24-48 hours after a new iOS is released so probably this won’t work for you anymore. You can never downgrade the baseband to 4.10.01 or lower even if you have the SHSH. Chip replacement is the only possibility if yours can’t be factory unlocked.
If you have an iPhone 4S, no, Apple pretty much blocked any method of downgrading the baseband or iOS for iPhone 4S.
iPhone 5? Zero possibility of downgrading of any sort (more details soon…)