With Amazon's(s amzn) first smartphone expected to be launched this Wednesday, we're getting answers to one of the biggest outstanding questions about the device: the Wall Street Journal is reporting that AT&T(s t) will be the exclusive United States carrier for Amazon's new smartphone.

AT&T is currently the wireless provider for Amazon's line of cellular Kindles and the two companies' close partnership has resulted in some interesting data plans for Amazon hardware -- for instance, offering a $50 annual LTE subscription back in 2012. Amazon could be taking advantage of the "Sponsored Data" program AT&T announced earlier this year. The two-sided billing program allows content providers -- like app or game developers, or in this case, Amazon -- to foot the bill for customers' data use. Amazon could conceivably pay AT&T to exempt data used for Amazon Prime music or video, or for advertisements like it displays on Kindle home screens.

In April, BGR reported that Amazon's smartphone could come with a feature called "Prime Data." That same report suggested that the device would be available exclusively on AT&T's network.

Leaks and Amazon's own promo teaser video suggest Amazon has been building an interesting device, featuring a new kind of 3D sensor and user experience. The device is expected to have four front-facing cameras and a "tilt-based" gesture interface with heavy 3D effects.

Gigaom will be covering Amazon's big reveal tomorrow in Seattle.