sorry, i saw your post late:(
unlocking a phone will just unlock the network lock, it does NOT change the firmware, your phone will still have the icon of at&t mall and links to at&t's website...so after u get the unlock code from at&t and unlock your phone, u need to flash the firmware of your phone so that u can get rid of the annoying at&t one.
unlocking and flashing(or debranding) are 2 different things.
good luck pal.:)