Come February, AT&T will raise the price for customers grandfathered into an unlimited smartphone data plan.

Subscribers who have managed to hold onto their unlimited plan since the iPhone 3G era will see a $5-per-month increase—AT&T's first in seven years.

"Consumers and businesses are using mobile data at record levels and the trend is expected to continue," the AT&T support site said. "To help ensure we continue to provide the best service for all of our customers, a small price increase is being made at this time."

The change increases monthly rates from $30 to $35. But, as 9to5Mac pointed out, this move opens the door for AT&T to make other changes, and perhaps more often than once every decade.

Unlimited, meanwhile, is not truly unlimited. Like many of its rivals, AT&T throttles users if they use more than 22GB of data in a billing cycle, which is admittedly a lot of data.

Those who don't want to pay the extra $5 per month can cancel their contract with no early termination fees within 60 days of the price hike. If you switch to a different plan, though, you cannot move back to unlimited. AT&T got rid of that in 2010, and is basically waiting for those grandfathered into those plans to drop them.

Other carriers are doing the same. Verizon recently announced a $20 raise for unlimited data plan subscribers, while T-Mobile raised its unlimited Simple Choice data price for new customers.