Microsoft has told BBC News that the firm is looking into reports of Windows Phone 7 'phantom data' transfers which some users have said that can be as much as 30 to 50MB per day.
The reports first emerged on Paul Thurrott's Windows Supersite with the Microsoft specialist also reporting unusually heavy traffic on his own personal Windows Phone 7 handset. "Microsoft? If this is your fault, as I suspect, you're costing people money on this one," said Thurrott.
Microsoft has previously not commented on the reports but told the BBC: "We are investigating this issue to determine the root cause and will update with information and guidance as it becomes available."
The issue is thought to relate to the devices sending the data via 3G even when Wi-Fi is available. Even so the level of unclassified data is unusual for the phones to be using with no indication as to what the mobile operating system may be doing.
Some users have speculated that the data is related to gathering metrics of performance and usage patterns in order to improve performance in subsequent updates, an approach not unusual in PC-based software although normally with permission being given by the user in advance.
At the CES show Microsoft gave some indication of impending improvements to Windows Phone 7 including the addition of Copy and Paste functionality present on competing smartphone operating systems iOS and Android.