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No, I don't think you'll find jailbreaking software in an app store that's only accessible by phones that are already jailbroken.
 
You won't find the jailbreak in cydia either. The come from servers that are usally run by say George Hotz or the Dev-team etc. Only use trusted sites. There is no jabreak 4.0 non will come out till it's offially released. Mouse never tips off the cat.
 
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