It's been a HUGE relief reading this forum, because the exact same thing happened to me a few days ago, and I've been freaking out. I'm currently completely locked out of my Itunes account. Can't make any purchases (not even with the credit I have), can't even make free app updates from my Iphone. At least now I know it's a general problem, and I'm not alone :')
I don't know what triggered this, though. I'm currently visiting family in Puerto Rico, but PR is a US territory, and has always used the US Store. PR is even listed as one of the states when I tried to input my cc info. And I copied the address exactly as it appears on my credit card provider.
grr. I e-mailed them, am awaiting a response, and very anxious, and very, very angry.