won't read USIM card from korea provider

Ok dell help me out, I purched the dell streak in Best Buy before i left to South Korea, I got my phone unlocked by AT&T. My issue is now that I just recently bought a phone with USIM card from SKY provider. I insert my SIM card into the Dell Streak and it doesn't read the card to register to their Network. What can be the problem, I have the phone on 2.2 froyo right now.