I just got mine activated today at 3:30p. Started the activation process at 7:30p Friday night. It took 7 calls to AT&T to straighten out my old rate plans, and a trip to an AT&T store to migrate my wife's non iPhone to a newer plan.
We were old AT&T wireless customers (before the merge to Cingular) and were on a grandfathered in shared-minutes plan that had been bought using a company discount. All those things worked against the iPhone activation.
Did you get an email that says you need to call AT&T to complete Activation?
If so, KEEP CALLING and pushing them to do a manual activation! If they tell you you just need to wait it out, REFUSE. All the reps I talked to early on didn't realize that when your plans are that screwed up, the automatic activation kicks you out and will not continue without manual intervention on their part.
My last call today, on a whim, and the guy did one thing on the computer, and literally 20 seconds later, I got the activation email, and was up and running. If I didn't insist on manual activation, I would still be waiting!
Good Luck!!!