Will an unlocked Iphone (originally purchased from AND unlocked by ATT) be able to be used in S. Korea?

Greetings,

I will be traveling to S. Korea in about 4 months (for about a year), and I currently have an iphone 4s purchased through ATT. I am still under contract. Since ATT is now unlocking their iphones for particular customers, I contacted them and asked if they would unlock my Iphone 4s, and they did. I received the email about a week ago on "How to Complete Your Authorized iphone Unlock". So, over one hurdle. So now that I am able to unlock the phone, will I be able to take it to S. Korea, insert a SIM card from a carrier there, and be on my way? There shouldnt be any problems right, or am I missing a step? I havent bothered to unlock the phone yet since I do not have a SIM card to check if it worked or not (or does that matter if I do it now or not??), but it shouldnt be an issue when I go overseas right?

I took a look through all of the questions regarding S. Korea but they were all before ATT made the decision to unlock their phones; so its not a legal issue or anything of the sort. I just didnt want to repeat an already asked question...

Thanks!

asv