Of the two models displayed, the Nokia Lumia 520 is the low end handset, which a quick perusal of the specs will confirm. To refresh your memory, the unit is expected to offer a 4 inch sensitive screen (in other words, don't insult it) with a dual-core 1GHz processor under the hood. 512MB of RAM and 8GB of native storage tags along for the ride. A microSD slot will expand the storage capacity on the phone, which does have a rear-facing 5MP camera. There is no front-facing shooter on the device.
The Nokia Lumia 720 supposedly has a 4.3 inch glass, a 6MP camera on back and a 2MP upfront. Otherwise, refer to the specs for the Lumia 520.
What everyone is waiting to see at MWC are the other two phones that Nokia is rumored to be unwrapping at MWC. One is expected to be a variant of the Nokia Lumia 920 with a thinner design and an aluminum body, codenamed the Nokia Catwalk. The other, codenamed the Nokia Laser, is believed to be a Windows Phone flavored version of the Nokia 808 PureView with a 41MP camera. One of the two recently visited the FCC, as we mentioned on Friday.
source: @evleaks via WMPoweruser