AT&T scored record sales the first day the iPhone 3GS hit store shelves, an internal memo shows.

The Apple smartphone, released June 19, was responsible for several milestones, including a "best-ever sales day" in the company's retail stores and the second-largest traffic day in the stores, according to the memo sent to all AT&T employees, and leaked to the Wall Street Journal's All Things Digital and MacDailyNews. AT&T said the iPhone 3GS was also responsible for the most transactions processed by its IT systems in a single day and the largest order day ever on att.com.

AT&T's exclusive contract with Apple is scheduled to expire next year, and the carrier is reportedly seeking an extension. In addition, there have been reports that Apple is talking with Verizon about carrying the popular device.

AT&T has certainly benefited from the exclusivity. Before the iPhone 3GS went on sale, the company said "hundreds of thousands" of customers preordered the device.

Nevertheless, users are criticizing AT&T over speed of its network and the company's failure to immediately take advantage of all the device's features, such as tethering and multimedia messaging. Tethering is the ability to run an laptop through the the iPhone's broadband connection. AT&T has said it plans to offer both features in late summer.

Apple said last month more than a million units of the iPhone 3GS sold the first three days it was on sale, matching the sales performance of the iPhone 3G launched the year before.

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