We caught up with Greg Sullivan -- senior product manager of Windows Phone -- for an early morning chat during Mobile World Congress. He was kind enough to give us an update on the state of Microsoft's mobile OS, which has apparently experienced a four-fold increase in sales since version 8 launched last fall and is taking share away from Android in the UK. We discussed the delightful user experience provided by lower-end Windows Phone 8 handsets like Nokia's Lumia 620 and asked how Microsoft plans to satisfy power users at the higher-end of the spectrum who are still missing critical features such as proper notifications, quick settings and CalDAV / CardDAV support (to name a few). It's clear that the company's aware of these shortcomings and is working to remedy most of them in a future release. We also talked about the ecosystem, what Microsoft is doing to improve app quality, how it meshes with Windows 8 / RT and whether the company is looking to expand its partnership beyond existing device manufacturers. Look for our full video interview after the break.