Microsoft said it's investigating a Windows Phone 7 software behavior that has the phone slurping up cellular data, even when the phone is connected to Wi-Fi.

The cause of this data use is not yet known, but the BBC points to a handful of reports that say it's a built-in feedback tool that's essentially phoning home.

If true, this type of behavior would not be out of place compared to other smartphone operating systems. In fact, Apple's iPhone came under similar scrutiny last year, with some users reporting large chunks of data getting sent in the wee hours of the night.

A Microsoft spokesperson said simply that the company was "investigating this issue to determine the root cause and will update with information and guidance as it becomes available."

Several years ago background data use would not have been as much of an issue, however within the last year, carriers like AT&T and Verizon have moved away from so-called "unlimited' data plans, to packages of data that can be purchased in allotments. (Note: Verizon still offers an unlimited data plan, but added a limited 150MB plan in October.) For consumers these represent a more economical way to buy into a smartphone purchase over the course of a long-term contract, but can carry steep penalties for overages.

With some entry-tier data plans hovering in the 150MB to 200MB range (depending on which carrier you're on), that amount can be reached quickly when normal use is mixed with this extra data polling, which is said to range from 30MB to 50MB of data per day.

Microsoft's first big update to its Windows Phone 7 platform is set to roll out to users in the next month or so. It's not yet clear whether that update will address this issue, or whether new software will be necessary to make any changes.