Microsoft says it is investigating claims from users that Windows Phone 7 handsets have been sending and receiving "phantom data" .
According to a report from the BBC, the software giant is to look into claims by users that the phones, which rival Apple's iPhone 4 and Google Android handsets, have been sending and receiving data without their consent.
Some users claim their handsets have sent "between 30 and 50MB of data" a day, making serious in-roads into data plan limits. Most of the complaints are reported to come from US users.
One Windows 7 phone user calling herself 'Julie G' told Paul Thurrott's supersite for Windows: "I received an e-mail from AT&T saying that I was close to my 2GB data limit which truly shocked me as I feel I do not use data that much."
Some users have speculated that the phones were sending feedback to Microsoft about their performance. Others suggested the handsets may be using a 3G mobile connection even when wireless networks were available.
"We are investigating this issue to determine the root cause and will update with information and guidance as it becomes available," a Microsoft spokesperson told the BBC.
Speaking at the recent Consumer Electronics Show in Las Vegas, Microsoft CEO Steve Ballmer told attendees that the company would soon release "a series of platform improvements" to Windows 7 in response to feedback from users.
"Windows Phone 7 is the best new phone out there,” Ballmer said. “As people try it, and discover its new features and beautiful hardware, they see the difference. They see how it makes everything from gaming to social networking to productivity better than on any other phone.”
Microsoft claims more than 1.5 million Windows Phone 7 handsets were sold in the first six weeks after the mobile OS launched in October 2010.