If you have been following me on twitter you probably already know by now that I believe that’s there’s no “Data Usage” bug in Windows Phone 7 that’s why I decided not to post about it when every other website went crazy over this story but yesterday’s official statement from Microsoft confirms my thoughts by claiming that this strange behavior apparently affecting only a handful of users is caused by a third-party service:
We have determined that a third-party solution commonly accessed from Windows Phones is configured in a manner that potentially causes larger than expected data downloads. We are in contact with the third party to assist them in making the necessary fixes, and are also pursuing potential workarounds to address the configuration issue in case those are needed. At this point in our investigation, we believe this is responsible for most of the reported incidents.
We are investigating additional potential root causes for the remainder of the reports.
A small (low single-digit) percentage of Windows Phone customers have reported being affected.
We are continuing to investigate this issue and will update with additional information and guidance as it becomes available.
So what is this mysterious third-party service?Well, it can’t be a third-party application given that they can’t run in the background at all (remember WP7 doesn’t support 3rd party multi-tasking) that the issue has been reported to happen when the phone is idle and the screen is off. The Push Notification service is handled by Microsoft so any suspicious third-party application behavior sending tons of data to it’s users would have already been detected and shut down by MS a while ago. I highly suggest you look at my Windows Phone 7 review where I describe all the connected services that are present in in the OS. But those are all first-party services and if Microsoft’s statement is to be believed they are not the cause of the problem. So what do we have left? Some people have guessed that it may be the Facebook service. I don’t think so thought, mainly because if this was the case; a lot more users would have reported the issue and also because Facebook content (and Live content too) is only synced with the device when the People Hub or Pictures Hub is opened. Which means that it can’t happen when the phone is idle. Just do the test yourself: Pin your own contact card to the home screen, go to Facebook (or Windows Live) and change your avatar picture. It won’t update the tile unless you open the People Hub or your contact card.
The most probable cause is Push Mail synchronization and in this case: Yahoo’s IMAP service. It has been reported in several forums way back in November that there seems to be an issue with Yahoo’s IMAP synchronization service which apparently consumes way more data than Google’s IMAP when setup on a Windows Phone 7 device:
I firmly believe that out of all the users reporting larger than normal data usage many of them don’t realize that Wifi is always shut down when the screen is off (unless the device is charging) or didn’t pay much attention to the vast number of data service settings in the OS (ex: that the Feedback service is always re-enabled when the phone is rebooted and a Marketplace download started on Wifi will switch to the Cellular data network if the Wifi signal is lost). But those who have really stupidly high Data Usage even after correctly setting up their phone are probably affected by the Yahoo IMAP issue and this fits with Microsoft’s official statement. This is obviously just my guess and I may be wrong but I just want to clarify the situation a little bit.
Update February 1st: Microsoft has officially confirmed that Yahoo Mail is the problem…