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How to Guide to Jailbreak iOS 4.2.1 with Greenpois0n RC 6 (Unteathered)

so i tried this and it was the only one that worked!! I think..greenpoisin never said jailbreak complete but it seems to have worked on my phone..it has cydia on it and i followed another thread on how to unlock it but when i put my sim in (tmobile) it just says "no service" . Please Please someone give me some advice

You will need to check that your baseband (modem firmware) is compatible. If you've upgraded to 4.2.1 via itunes without using a custom ipsw then it wont be...