dstates writes "What happens when Apple ships 100,000 iPhone 4S in a day? Answer, 100,000 users all try to activate their new phones. AT&T's activation servers are struggling under the load. Apparently Verizon and Sprint are doing a better job keeping up with the load."
Adds an anonymous optimist: "The solution? Call AT&T by dialing 611 and talking to an operator to perform a manual activation with your IMEI and SIM card #, works every time!"