Hot on the heels of our interview with Stephen Elop, we sat down with Marko Ahtisaari — head of design at Nokia — to chat about the Lumia 720 and Lumia 520 Windows Phones along with the basic Lumia 301 and 105 models. The four handsets, which were introduced today at Mobile World Congress, share the same design language — in fact, this marks the first time the company’s extending its signature Lumia look and feel to devices costing as little as €15 ($20). We discussed the evolution of Nokia’s current aesthetic from the Nokia N9 (and the Lumia 800) to the present day. Mr. Ahtisaari touched upon the engineering challenges involved in building affordable smartphones like the €139 ($184) Lumia 520. We talked about the Lumia 720′s thin and light unibody shell and the Lumia 620‘s double-shot color scheme, then asked how the Asha design language fits into the current lineup. Curious about the answer? Watch our video interview after the break.