Starting September 6, any customer purchasing a smartphone or upgrading to a smartphone with AT&T will be required to subscribe to a $30 monthly data plan (in addition to a voice plan). The change doesn't affect existing customers until they need to upgrade their phone or plan.The news was first dug up by Boy Genius Report, but I was able to get an AT&T spokesperson to verify the accuracy of the report.

AT&T's official statement reads as follows:

Smartphone users tend to consume a higher amount of data services, like advanced e-mail, mobile Web, applications and more. Being able to take full advantage of these features without having to worry about a fluctuating or unusually high bill generally leads to greater customer satisfaction, so effective Sept. 6, smartphone customers will need to subscribe to a data plan, as the vast majority of customers already do.

Is this really a big deal? Well, to a few, it probably will be, but the majority of smartphone users are already subscribed to monthly data plans. iPhone users, for example, have long paid the $30 monthly data fee, as have BlackBerry users. They will experience no change.

Some other things to keep in mind. The $30 monthly data fee isn't required for regular feature phones, including QWERTY-enabled messaging phones. Smartphone include the iPhone, BlackBerries, Windows Mobile-based devices and certain S60 phones.