What you see below is what is believed to be a leaked roadmap of Windows Phone and where Microsoft [MSFT] is taking it.
The first two boxes (WP7 GA and Mango) have already passed in that we now see smartphones running Windows Phone Mango. The next step which is dated Q2 2012 will be for Tango which looks to be a minor update in terms of changes to the operating system other than being able to function on lower end and more budget devices.
After Tango comes Apollo which is the step which it looks like things will get interesting. It appears that by this time next year Microsoft will be pushing business devices more as well as more high-end devices which could include faster CPUs (dual or quad core) along with better screen technology pushing closer to HD.
WP7 is still in early days and although some numbers are looking good such as the rate at which the Marketplace is growing, it still has a long way to catch up to Android and iOS in terms of devices activated per day as well as the whole size of the app store.