Unlocking Optus Pre-Paid Question

[DBAH0]

I've got a prepaid phone both in the U.S (with A,T &T pay as you go) and in Oz with Optus (also prepaid).

I took my phone from Australia to U.S to use because it's a better one however. Would I need to call up Optus first to unlock my phone, before I take the sim card out, and put the one from my U.S phone in my Australian phone to use?

 

[STFUJEFF]

had one London to Australia
They gave me the code via email to unlock it.