Thank you vonsamurai! I just called at&t, my service provider, and told them what you told me. They said ok. I got the code and just unlocked my phone!!!
I also found the similar thing on at&t's forum and copy it to this forum so that more people can know about this. For those people, like me:), really want to unlock their phones, you really need to call your provider for the unlock code to unlock your phone. No matter what phone you have and No matter what provider you have and No matter what country...you just need to do it:p so u don't waste your time looking hard for solutions online to unlock your phone. ASK FOR INSTRUCTION ALSO IF NEEDED BECAUSE DIFFERENT PHONE OR PROVIDER REQUESTS DIFFERENT INSTRUCTIONS UNLOCKING YOUR PHONE! For more info, read this thread i posted: LISTEN UP AMERICANS!!! (Those who wanna unlock their W580i from ATT) - Top Sony Forums