Donwgrading baseband is almost impossible currently. It is possible to downgrade the iOS Firmware if you had saved your SHSH blobs, but this is unsupported by Apple and you have to use Cydia&#39;s servers.<div><br></div><div>

All in all, if you have an iPhone 4 with a baseband above 01.59.00, you will not be able to downgrade and you will not be able to unlock.</div><div><br></div><div>With the iPhone 3GS made prior to 2011, you are able to &#39;upgrade&#39; to the iPad 06.15.00 and unlock. Though you may end up losing GPS capability.</div>

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