This is not a surprise.
You would think 5 phones later, AT&T would be more prepared for days like this.
Then again it hardly seems worth building out a server network to handle crush capacity one day a year. This peak is probably like 10,000x normal daily loads. If I were the ATT CFO, I would not approve a budget that builds to that peak.
Now if ATT only ran their activation servers on the Amazon Cloud maybe they could scale better for a day.