the new Blue version of Windows Phone featuring IE11, it also could be the minor GDR2 update that also is expected. Back in March, we brought to your attention a job posting for Microsoft seeking a test engineer for Windows Phone 9 which is a separate project than Windows Phone Blue. The latter is more about merging different variants of Windows. Last month, speculation had Windows Phone 9 launching in October.
source: @ailon via WMPoweruser