[Q] HTC HD2 unlock problem

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http://forum.xda-developers.com – I am looking at purchasing a HTC HD2 from ebay. Unfortunately, it was from a "batch of phones that had left the suppliers locked" The supplier eventually offered a refund and he also, maybe inadvertently kept the phone as well. When he now puts in the SIM card the message reads --"Service provider is locked. Please input unlock code." Apparently you can have these unlocked, but one site states that "This service will NOT remove your phone’s security lock" Can somebody please explain to me what this means? Is it correct that you can only enter the unlock code 5 t (HowTos)