Well, my excitement for the morning has passed. I woke up to find my cell phone service cut off and, upon further inquiries, that I owed almost $400.
After paying enough to get my service back, I was able to investigate my online bill. Seems like the main problem was that I was being charged $1.49/minute for my calls to the UK instead of the better $0.08 rate that I pay a little bit extra to receive. And, since that's the difference between $8 and $150 for my recent calls, it was dramatic. Customer service was great and fixed everything right away.
So, yay for AT&T and your service (although I may be shouting about a reactivation fee if I see one, for the bill that I never received)!