Unlocking 3315

I bought to use in Europe a Nokia 3315 which is supposed to be unlocked (according to the seller in Chicago) despite that the Box reads "this handset is SIM-locked and can only be used with a SIM card provided by SMART Communications." However, when I introduce a SIM card, I get the message "SIM card not accepted".
I'm not sure whether this phone is DCT3 or 4 and how to proceed to unlock it. I have IMEI and network code from SMART Communications. Please advise.
Thanks and regards.

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