Some Windows Phone 7 users have complained about excessive data usage on their device, even when the handsets were idle, making Microsoft start an investigation on this matter. Smartphones were downloading up to 50MB a day for no apparent reason and now the Redmond giant blames it all on a third party solution.
Said solution is commonly accessed from WP7 and configured in a way that could lead to large data leakage. MS has already contacted that third party in order to fix the issue, but they didn’t want to mention its name. Wmpoweruser suspects this could be the Facebook integration on the handsets, but that’s a speculation for now.
Investigations continue on this issue.