iPhone 4 international unlock question

I need this question answered quickly. So i contacted Sprint ask them to unlock my phone so i can use international sim. They said sure but for you to be able to use it, i will have to update to latest iPhone version and I do not want to do that.

are they lying, it doesn't make sense as to why updating to the latest version will enable the unlock on their side to my phone. also is there a way to be able to use the unlock without updating to latest version?

Source: http://forums.macrumors.com/showthread.php?t=1396511&goto=newpost

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