The Nokia Lumia 710 represents Nokia's initial push into the US market with Windows Phone, and some are quick to paint it as a failed move by Nokia.  Why release the mid-range product when CES (and their assumed high-end entry into the US market) is right around the corner?  The wireless market is turbulent indeed, but given the affordable price - $49.99 with a two-year agreement - the Lumia 710 an option that's worth considering.  It's not going to win over any die-hard smartphone users, but in comparing it to the HTC Radar 4G, Samsung Gravity Smart, and the crop of other mid-range choices on T-Mobile, it would be high on my list.  Here's why:

• As with any Windows Phone, the 1.4 GHz single-core Snapdragon processor is more than adequate to handle daily tasks.  I've seen no unusual lag on this device, which is the beauty of Windows Phone - that is, the performance is pretty much consistent across the board.  The Lumia 710 doesn't have a front-facing camera, 8-megapixel camera, or a metal body, but it performs largely on-par with the high-end HTC Titan.  I can't underscore this enough (and you'll see this theme throughout my impressions) - you're spending less money, but you're still getting consistent performance on the front-end.

• The Lumia 710 screams "mid-range" in its build quality.  Made entirely out of plastic, you'll find the power button, 3.5mm headphone jack, and microUSB charging port on the top, along with the volume rocker on the right spine.  Oddly enough, the Lumia 710 has physical Back, Home, and Search buttons below the display.  The 3.7-inch display may be on the smallish side for some, but I find it to be a nice size in comparison to the 3.2-3.5-inch alternatives in the same category.
• I like the simplicity of Windows Phone, though the ecosystem has a ways to go before it can compete with the likes of Android and iOS.  Still, the design is refreshing, and a welcome change for those that value form over functionality.  Mango brings some nice improvements over the initial build, such as live tiles that will display your information and the ability to group inboxes into a unified app.  In addition to the usual T-Mobile stuff like MyAccount and T-Mobile TV, you get ESPN, Nokia Drive, XBOX LIVE, and Microsoft Office.  Nokia Drive is an exceptional application that fills the "Where's my navigation app?" question I've been asking for some time with Windows Phone.

• There are some OS limitations that carry over into Mango, such as the inability to consistently display network/battery life information and the resizing of tiles.  As it stands, you can't control which tiles show up as squares and which ones show up as rectangles on the main screen.  I'd also like to see some more personalization in future builds, like more theme colors and the ability to add a wallpaper to the homescreen and app sections (because that black/white screen gets old).
• Lumia 710 supports T-Mobile's HSPA+ network and can attain theoretical speeds of 14.4 Mbps, though you'll probably never see them get that high.  In testing, I've seen download speeds range between 2.1 and 3.8 Mbps.  I'm still doing full battery tests, so stay tuned to see if the 1,300 mAh pack can make it through the day.

Unlike Android, high-end versus low-end Windows Phones don't really distinguish themselves in the specification department; they do it in design.  Regardless of whether you spend $49.99 or $199.99, you'll get a 1.4 GHz or 1.5 GHz processor, a five or 8-megapixel camera, and the same build of Windows Phone 7.5.  Considering the alternative - mid-range Android phones that pack between 600 MHz and 1 GHz processors and no guarantee as to whether you'll get a current build of the OS or not - the better value proposition here seems to be the Windows Phone. 

Nokia's Lumia 710 may not win anyone over in the design department, but it is the most feature-packed $50 handset that I've seen in some time.  And while it remains to be seen what Nokia will announce at CES, I'd recommend it to any T-Mobile customer that's shopping around in that price point.