Online retail giant Amazon is set to unveil a new piece of hardware at an event in Seattle on Wednesday. 

The company is widely expected to reveal a smartphone that will give it yet another avenue to appeal directly to consumers. Despite months of apparent leaks, rumors and innuendo, the details are still pretty hazy. But here's what we think we know. (Disclosure: Amazon CEO Jeff Bezos owns The Washington Post.) 

It is a smartphone. Rumors of an Amazon smartphone have swirled for years, so everyone is assuming this new hardware is a phone based on the promotional material Amazon has released so far. BGR, which has a pretty strong track record of coming through when it comes to Amazon leaks, even claimed to have photos of a prototype device.

There are some pretty compelling reasons that Amazon would want to break into the mobile phone business. While the company got its start selling physical books and grew to sell almost any item in the world through a single Web site, Amazon has increasingly invested in digital services, from cloud computing to e-books and online video rentals. Its forays into the hardware space, including the Kindle line and FireTV, serve as direct portals between consumers and Amazon's online marketplace. But without a smartphone, it is missing out on chances to sell to customers when they're on the move.

It's still technically possible that the Amazon hardware announcement scheduled for today is something else entirely. But basically every tech journalist out there is going to feel like a huge idiot if the company reveals it is releasing a game controller for FireTV or some other contraption.

It's a 3D smartphone with a gazillion cameras. Along with the apparently leaked photos in April, BGR reported sources claiming the rumored phone had a total of six cameras -- some of which enables a glasses-less 3-D experience. Presumably, that 3-D effect and rumored tilt controls could be why people are moving their heads and freaking out in this Amazon-released promo video:

According to TechCrunch, the technology behind this anticipated feature comes from Japanese company Omron’s Okao Vision face sensing system, which it reports has been modified by developers in-house at Amazon. The software pack associated with the Okao Vision system "can also recognize faces and facial attributes to estimate a person’s gender, age and ethnicity" per TechCrunch, but the outlet did not believe Amazon was planning to roll out these features in its initial smartphone.

An AT&T exclusive? The Wall Street Journal reported Tuesday that the device would be exclusive to AT&T customers at its initial launch -- much to the chagrin of T-Mobile CEO John Legere. This isn't too much of a stretch: Amazon already uses AT&T for data plans for its Kindle e-readers and tablets. Plus, AT&T has a history making exclusive deals. While the HTC First "Facebook phone" flopped, AT&T did pretty well as the exclusive carrier of Apple's iPhone for its first few years on the market.

The killer app could be "Prime Data." According to an April report from BGR, the smartphone will come with a "unique wireless data plan," tentatively called "Prime Data." 

"Prime" here likely refers to the Amazon membership program, which initially just offered free two-day shipping on many items for an annual flat rate, but has since added new features over the years, including streaming video and a lending library of e-books.

Another hint for what "Prime Data" could be: In January, AT&T announced a "sponsored data" service in which certain data charges from consumers could be billed to a sponsoring company -- similar to how calls to a 1-800 number works.

It doesn't seem too crazy to imagine that Amazon would seek to tie the benefits of Prime and AT&T's sponsored data to its entry into the smartphone market. If "Prime Data" is a deal with AT&T to exclude Amazon content from mobile data caps, that might be a powerful incentive to get users interested in the hardware -- and interested in buying Amazon content. Plus, it might explain why Amazon would agree to limit its device's potential audience to one carrier at launch.