AT&T will begin selling the highly-anticipated Nokia Lumia 900 smartphone on April 8th for a meager $99 (with obligatory two-year contract). The bargain price for a flagship device may boost both Nokia and Windows Phone, but it’s not the only device offered by AT&T for $99. Before choosing, consider the alternatives and see how the Lumia 900 stacks up against the $99 competition.

It is highly unusual for a marquee smartphone to be offered at such a disruptive price. Apple’s iPhone 4S, and the Android-based Samsung Galaxy S II Skyrocket are both $200 with two-year contract. If anything, the trend seems to be going higher, not lower. The Samsung Galaxy Note “phablet” is $300 from AT&T with contract, and flagship Android smartphones like the Motorola Droid Razr Maxx and Samsung Galaxy Nexus are both $300 with contract from Verizon.

The $100 price point is generally reserved for older devices like the iPhone 4, or the Motorola Atrix 2. So, if you’re in the market for a new AT&T smartphone, and you only want to spend $100, is the Lumia 900 the best choice, or would one of the other $100 options serve you better?

With the iPhone 4 you get a smaller display than the Lumia 900 or Atrix 2—3.7 inches compared to the larger 4.3 inches. But, the display is Apple’s “Retina” display with ridiculously high pixel-density for crisper text and clearer images. The iPhone 4 has only a 5 megapixel rear camera capable of capturing 720p HD video, and a VGA-quality front-facing camera, and now that it is no longer the premier iPhone model, it is only available with 8GB of internal storage.

If Android is more your style, the Atrix 2 is a perfectly capable smartphone as well. The Atrix 2 is the only smartphone among these three that sports a dual-core processor. It comes with the same 8GB of storage as the iPhone 4, but it is expandable up to 32GB thanks to an SD memory card slot. It has an 8 megapixel camera capable of capturing 1080p HD video, and it is a 4G device for faster wireless broadband.

That brings us to the Nokia Lumia 900. The Lumia 900 also has an 8 megapixel rear camera, and 4G connectivity. The display is vivid with a Super AMOLED display, and strong thanks to Corning Gorilla Glass. It has more storage than the other two out of the box with 16GB, but lacks the expandability to match the Atrix 2. At a time when most smartphones have moved to dual core, and cutting edge devices are equipped with quad core processors, the Lumia 900 is driven by a single CPU core.

One of the primary factors in choosing, though, may be the other devices and applications you use. If you use Mac OS X and/or have an Apple iPad, you may lean toward the iPhone 4 for the consistent experience, and the ability to share many apps among your devices. If you rely on Google Docs, Gmail, and other Google products, the Android device may make the most sense because of its seamless integration with the Google ecosystem.

But, if you use Windows, Microsoft Office, SkyDrive, and other Microsoft tools and products, the Lumia 900 may be the way to go. Microsoft has developed a solid competitor with the Windows Phone platform. Windows Phone is unique, and innovative, and the Lumia 900 will most likely give it some badly needed momentum.

When you walk into AT&T with your $100 on April 8, though, think about the pros and cons of the different devices, and how your smartphone will mesh with the other tools you rely on, and choose the one that best meets your needs.