While it's still not so clear what Nokia would be brining at the Mobile World Congress (MWC) this month, there seems to be a new Lumia device which the Finnish mobile phone maker is yet to announce. The mysterious device appeared in an ad designed to showcase the Lumia 920 on Dutch carrier KPN. The Lumia device features rounded corners and curved back, which is definitely not of the Lumia 920 design.

First noticed by My Nokia Blog, the yellow colored device seems to have a slime profile and the common guess is that it would be one of the devices Nokia plans to unveil in a couple of weeks at the WMC.

Though the shape of the device does suggest a close similarity with Nokia Lumia 822, it's already known that Lumia 822 is exclusive to Verizon and does not come in yellow. In addition, the mystery device features a headphone jacket that is different from Lumia 822 model. The smartphone appears to be a combination of Lumia 822 and the Lumia 620, which makes us speculate that the company is working on yet another budget Windows Phone. It's also possible that the device would not be any of the rumored models, but can very well be a mock-up or even a digital edit.

Recent rumors have it that Nokia may release two new handsets - Lumia 720 and Lumia 520, at the MWC. Nokia Lumia 720, codenamed 'Zeal' will come with a 4.3-inch ClearBlack display, 1GHz dual-core processor, 8GB of internal storage, 512MB of RAM, 6-megapixel rear-facing and 2-megapixel front-facing cameras. The device will support HSPA+ networks, run Windows Phone 8 and has a microSD slot for storage expansion.

Nokia Lumia 520 which is codenamed 'Fame' will feature a 4-inch Super Sensitive Screen, 1GHz dual-core processor, 8GB of internal storage, 512MB of RAM, and a 5-megapixel rear-facing camera. The device will not have a front-facing camera. Lumia 520 will run Windows Phone 8 and has a microSD slot for expansion.

Take a look at the ad: