Should I update my iPhone 42 to iOS 7 or wait for a 6.1.3 jailbreak?

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I can't help you but, How the Hell did you get an iPhone 42? Let me know please.

It depends what you want the jailbreak for. Most of the features we've enjoyed in previous jailbreaks are now features within iOS 7 itself.

If you want to get free premium apps, then that's another story.

There should be an iOS 7/7.0.1 jailbreak out soon, so you may as well update and see if you actually need to jailbreak any more.

If you decide to jailbreak, check here for the genuine ones; http://www.isthereajailbreak.com/