I know this thread is more than two years old, but I'm experiencing the same problem as the OP. I had to restore my iPhone 2G and now when I'm trying to activate it, it says "iPhone activations are unavailable at this time". By the way, it's been saying that for almost a day. AT&T CS rep told me it's an iTunes issue since it's done via iTunes. I didn't even wanna go there.
But anyway, what else can be done besides waiting for God knows how many days?