Lumia 520 is the cheapest Windows Phone 8 for Nokia, starting at $184, with a 1GHz dual-core processor, 512MB of RAM, 8GB of storage, a 4-inch WVGA screen and a 5MP camera. It weighs 124g, it has a 2D hardened glass and it is also ideal for touch while wearing gloves. It will be released in five colours (cyan, yellow, red, black and white) and it is expected during the next quarter. It seems like a pretty decent phone for its money, with Nokia's experience and Micorosft's ambitious Windows Phone 8 being a great combination.
As for Lumia 720, it is a bit more sophisticated, with a 6.7MP camera, a 4.3-inch screen, a 1GHz CPU, 512 MB of RAM, 8GB of storage and it will be priced at $329. Lumia 720 will also have a Carl Zeiss lens and f/1.9 aperture, also focusing on the front camera with an f/2.4 aperture, which makes it an ideal choice for everyone that loves taking decent pictures with a smartphone. It supports NFC and it also allows wireless charging with a snap-on cover. Lumia 720 will also be released in 5 colors and it is expected mostly in Asia and some countries in Europe. There are already some users from the U.S. that found Lumia 720 attractive, although it seems that it won't be available for them.
Nokia is trying to recover on the smartphone market, targeting for now the low and mid budget users who used to purchase affordable Android devices. It's up to them to persuade them to trust them.