The iPhone 3GS has been available since June 19, but Apple only recently re-activated the inventory tool. Last summer, users were told to use the tool after 9 p.m. local time each day to check availability for the next day. This year, there is no such instruction, since the tool has been changed to offer better information.

"You can check the most up-to-date availability right here," said Apple on the tool's Web page. "Shipments of iPhone 3GS arrive most days and availability is updated hourly."

All stores currently have the $99 8GB iPhone 3G in stock, Apple added.

AT&T, which last year also ran through its inventory soon after the iPhone 3G's July launch, and took much longer to restock, has some spot shortages in its 2,200 retail stores as well. The carrier, however, was vague about the extent of the problem.

"There are AT&T stores that do not currently carry iPhone," AT&T said in an message accompanying its . The remainder of the text was identical to last year: "This store locator is made specifically for finding iPhone at an AT&T store. It does not, however guarantee that there will be iPhones in stock at the particular store at this time. To make sure iPhone is at the store closest to you, call that store's number."