The baseband is definitely one of the key points of the iPhone terminals coded on a mobile network because depending on the software version of this component we can do or not decode the terminal. As you already know very well, for the iPhone 3GS you cannot downgrade the baseband and for the iPhone 3G it can only be done on terminals produced until September 2008, so a very small number of people can downgrade the baseband on old terminals. With iPhone 4, the situation is different because the device downgrades the baseband under certain conditions. More precisely, the terminal "aligns" the software version of the baseband with that of the current version of iOS available through iTunes. That is, at the moment we have iOS 4.1 in iTunes and baseband 02.10.04, but if we update to iOS 4.2 beta we update the baseband to version 03.10.01. On the old terminals, you could not downgrade the baseband in any way, but on the iPhone 4 you can do this when you restore to the current version of iOS. Taking the above example, the baseband 03.10.01 corresponding to iOS 4.2 beta 3 will be downgraded to version 02.10.04 when you restore to iOS 4.1 via iTunes.
This downgrade is ONLY possible if you have NOT modified the Windows hosts file to use the SHSHs from the Cydia server. If this change is made, then the baseband downgrade does not take place. The possibility to downgrade the baseband has existed since the launch of the iPhone 4 and there are no signs that Apple will stop it soon.
