Nokia Lumia 720, 520 Stake Windows Phone Middle GroundNokia Lumia 720, 520 Stake Windows Phone Middle Ground

Nokia's Mobile World Congress announcements may have disappointed those hoping for the Finnish firm's next flagship device, but they prove Nokia is committed to serving a broad range of customers.

The company took the stage this week to reveal the Lumia 720 and Lumia 520, two middle-of-the-road smartphones that run Microsoft's Windows Phone 8 platform. Neither is flagship material, and they instead fill empty spaces in Nokia's offerings.

The Lumia 720 is a midrange device that has a 4.3-inch display with Nokia's ClearBlack technology. The glass is curved so that it forms a smooth surface on the front of the phone. It makes use of the unibody style that Nokia has come to prefer, which means the battery cannot be removed. It has a memory card slot, and the camera features a Carl Ziess f/1.9 lens for better low-light performance.

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The 720 will not be sold in the United States. In order to keep the price down, it is targeting markets that don't yet have LTE 4G networks. This means the 720 will likely serve as Nokia's high-end device in emerging markets.

The Nokia 520, however, will be sold in the U.S. by T-Mobile USA. It is an entry-level Windows Phone 8 device that includes a 4-inch display that can be used with gloves on. It is powered by a 1-GHz Snapdragon S4 dual-core processor and includes a 5-megapixel camera, 8 GB of storage and a microSD card slot. It will reach stores during the second quarter, though pricing hasn't been revealed. Given the specs and cost of T-Mobile's other Windows Phone devices, the 520 will likely sell for $50 or less.

Beyond these two Lumia smartphones, Nokia announced several ultra-low-end devices for emerging markets, the 301 and the 105. Both are simple devices with few features other than basic telephony and messaging.

It has been about six months since Nokia announced a flagship device, the Lumia 920. The 920, sold by AT&T in the U.S., is still just reaching some markets around the world and clearly has some life left at the top of Nokia's smartphone heap. With the 720 and 520 added to its stable, Nokia now has devices in the 900, 800, 700, 600 and 500 range, each with clear differences in terms of features and price points. Covering such a range of prices with these phones is exactly what Nokia needs to do in order to get its phones into more hands.

Nokia isn't expected to name a successor to the 920 for at least a few more months.