According to WPCentral, WindowsPhone8 is already in testing. They’ve spotted some WindowsPhone8-running devices logged in a social app called “I’m a WP7!” which records and displays the percentage of different WP7 versions (and WP8 too, as it seems). The new OS, dubbed “Apollo” was scheduled for early 2013 but it might come sooner given that there are already running versions of it around.
Check out the full article on WPCentral.
