According to Engadget, a VP from Nokia is talking about the release of Windows Phone 8 (aka Apollo).
Michael Halbherr, Executive VP for Location and Commerce, told us that it’ll launch in mid-2012 and be a "very different game" to Mango — hinting that Apollo actually refers to Windows Phone 8 rather than any mere decimal increment.
That makes sense since it looks like Microsoft is following Apple’s lead here – a major update every two years and an incremental update every other year. So we had WP7 at launch. One year later Mango (7.5). Next year it’s Apollo and so on. And like the NoDo update, in the next year we’ll presumably see the Tango OS update that has some incremental changes and permits lower end devices.