For the record, I was able to get my BIS account registered to me, and received the service books and HRT.
However, my icons for MediaNet and other AT&T-specific stuff are displayed as T-Mobile icons, not AT&T icons. Also, all the splash screens still say T-Mobile. A tech I talked to said that I would need to install AT&T's OS to fix it, but when I tried that, it wouldn't update.
Would I need to do a complete wipe/uninstall in order to get these icons back?