AT&T will reportedly be the exclusive carrier for Amazon’s smartphone

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.