I discovered tonight that SBC's DSL tech support has been outsourced to India. They were very nice, but the first person I spoke to wasn't particularly helpful. I finally spoke to someone else who was willing to trust me and not follow the script. She couldn't tell me that they were in India, just International, but when the second lady had the same accent as the first, it was pretty obvious.
It still isn't clear exactly what happened, but it looks like their authentication server decided to forget my passwords. That would have been the first thing I would have checked when a user is reporting an Access Denied error, but I'm not in tech support.