There is no pin code to unlock the sim for other carriers. Sprint uses a tool that pushes the update to your phone via OTA. The code that you got was most likely the MSL. Witch is used for reprograming the CDMA side of the phone. But if you don't want to take my word for it all gsm phones that use a lock code prompt for the code only when a sim from a different carrier is in.(code needs to be enter only one time) If you put a sim in and don't get the error "invalid sim" something of that sort then your phone is already unlocked. also the phone will work with us sim cards.
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