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jRin.net reviews the RebelSim iPhone Activation Sim
to check out the full review and find how to buy these SIMs
This SIM card allows you to bypass the phone activation screen on any iPhone (2G, 3G, 3GS, 4, etc). It doesn’t actually activate it, but it allows you to bypass it in the event that your iPhone is locked and you don’t have a SIM for the particular carrier it is locked to (in order to “access” the phone, in other words, bypass the activation screen which in turn can allow you to then spirit jailbreak the 3GS or older)