Greg Sullivan, Microsoft’s Senior Marketing Manager, was on hand at this week’s Windows Phone Summit to answer questions about the announcements. After the keynote, he stuck around to show off the Windows Phone 7.8 update running on one of Nokia’s Lumia 900 handsets. In our video above, Sullivan can be seen demoing the changes to the Start screen (note the mention of the slightly modified – and currently buggy – app list). He then went on to discuss the challenges facing Windows Phone and how Windows Phone 8 will meet these issues head-on. The latter half of this conversation can be seen after the break.