For iPhone 3G/3GS, if you accidentally upgrade your device and let your baseband reaches 06.15.00, you will be locked there forever. But now thanks to our famous hacker, MuscleNerd had tweeted that “Made great progress yesterday on downgrade from BB 06.15 (for 3G/3GS owners who got officially unlocked). All the pieces are there 
”
Even though the downgrade tool is not yet release but learning from the tweet, we can assume that it will be officially released soon.
We will keep the matter in hand and update once it is available.
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