hi thunderzzz....
This is the response from Sprint:
"I can give you the Master Subsidy Lock code that you can give to the next carrier. That carrier can attempt to use this code to unlock the device."
They gave me the MSL code.
I had taken a backup, erased the iPhone, inserted a GSM SIM card and tried to restore the backup. But after inserting the new SIM, it says that "The SIM card inserted in this iPhone does not appear to be supported. Only compatible SIM cards from a supported carrier may be used to activate the iPhone. Please insert the SIM card that came with your iPhone or visit a supported carrier store."
Do you have any idea regarding MSL code ?