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open the phone, find the antenna, remove it, replace with antenna from gsm enabled , phone, and reflash the baseband. If you dont have gsm antenna, remove cdma antenna, and reprogram the signal to accept gsm, it can be done, as there are grey market businesses, that are buying cdma phones, shipping them to china, and 3rd party factories are doing this exact thing.
 
What steps are needed to unlock a Sprint iPhone 4 to work..

Well it hurts you my friend, but sprint phones can’t be unlock just because they don’t have IMEI number.
 
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