Andy Lees — long identified as the man leading Microsoft's mobile charge — has been moved out of his position as the head of the Windows Phone business, according to AllThingsD. He's not being demoted, though: he'll still be reporting directly to Steve Ballmer, albeit in a more nebulously-defined role working "on a time-critical opportunity focused on driving maximum impact in 2012 with Windows Phone and Windows 8," according to an internal memo sent out by Ballmer himself. Though there's no immediate direct replacement for Lees at this point, Terry Myerson — who leads Windows Phone on the engineering side — will be picking up Lees' tasks, and it stands to reason he could become a full-fledged Lees successor in the long term.
Update: Microsoft has posted Ballmer's memo, confirming AllThingsD's information. Also notable is that Terry Myerson will actually be taking on all of Lees' responsibilities at Windows Phone, not some subset.