The HTC 8X is thin, weighs 4.6 ounces, and has a contoured, colored, easy-grip case, whereas the Lumia 800 is thick, weighs 5.1 ounces, and has a blockier all-black case. The HTC 8X is much more comfortable to hold. Both have 4.3-inch screens, but the HTC 8X has a higher-resolution display (342 pixels per inch versus the Lumia 800's 217 ppi). Both use the 1.5GHz Qualcomm Snapdragon CPU. Both have an 8-megapixel rear camera with LED flash. The HTC 8X has a 2.1-megapixel, 1080p front camera whereas the Lumia 800 has just a 1.2-megapixel, 720p front camera.
The HTC 8X's screen is crisp, and the color balance very nice when playing back movies. Its speakers also produced clean, loud, well-balanced audio, despite their tiny size. The Lumia 800's screen is not as bright, resulting in muddier video, and its speakers are quieter and produce flatter sound than the HTC 8X.
The HTC 8X has either 8GB or 16GB of storage, and no expansion capability, whereas the Lumia 800 has just 8GB of internal storage but can accept an SD card with up to 32GB of additional storage. Both support 5GHz and 2.4GHz Wi-Fi networks. But neither has video-out capabilities as iPhones and many Android smartphones do. Battery life for both is adequate, with a full day's use per charge. The HTC 8X's battery rundown is similar to Android: It lasts about 24 hours when idle, like most Android smartphones, whereas the Lumia 800 uses little energy when idle, providing several days of power, like an iPhone.
Lumia 800-series models are available for AT&T (as the Lumia 820), T-Mobile (as the 810), and Verizon Wireless (as the 822), and the HTC 8X models are available for AT&T, T-Mobile, and Verizon. Keep in mind that T-Mobile has generally poor coverage; both of my test devices were the T-Mobile models, and I frequently couldn't get data service in either San Francisco or the Central Coast region of California for the week I used them. T-Mobile also lacks LTE service, so the Lumia 810 and the T-Mobile version of the HTC 8X don't have LTE-capable radios.
Although the Lumia 800 series skimps on the hardware side, it does come with a raft of useful Nokia apps -- including Transit for mass-transit routing, Creative Studio for enhancing photos, Cinemagraph for animating photos, Panorama for taking auto-stitched panoramic photos (a feature available in several iOS 6 and Android 4.x smartphones), Transfer My Data for Bluetooth copying of contacts from other devices, and the beta Drive+ for GPS navigation. The HTC 8X has a few basic extras of its own, including a unit converter, flashlight, and photo enhancer.