Apple's retail stores reported shortages of some models of the new iPhone 3GS Sunday, according to the company's own inventory tracking tool.

The shortages were a milder repeat of last summer, when Apple's stores quickly exhausted supplies of the then-new iPhone 3G, a situation that persisted for several weeks until the company could refill the pipeline.

On Sunday, Apple's stock-checking tool indicated that 13 of the 211 stores in the U.S., or 6% of the total, were completely out of the iPhone 3GS.

Another 31 stores, or 15%, had only one of the four models for sale.

The hardest-to-find iPhone 3GS was the $199 white 16GB model, which was out of stock in 121 stores, or 57% of the outlets. Supplies of the $299 32GB black iPhone 3GS were also short, as 84 stores, or 40% of the total, reported it unavailable.

Customers Sunday were most likely to find the $199 black 16GB iPhone 3GS and the $299 white 32GB model in stock: Just 23% of the stores were out of either of those configurations.

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 online store finder.

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."

Best Buy and Wal-Mart are also selling the iPhone 3GS. However, neither sells the iPhone online or offers any information about availability online. Instead, customers must call or visit a brick-and-mortar store to see whether the smartphone is in stock.

Before the June 19 launch, AT&T and Best Buy said that they had exhausted their pre-order supplies of the iPhone 3GS.