AT&T (NYSE: T) confirmed that it will increase the price of its legacy unlimited data plan by $5 per month, to a total of $35 per month, starting in February. 9to5Mac first reported the news, citing an unnamed source, and an AT&T representative subsequently confirmed the price increase to FierceWireless.

"Our unlimited data plan customers continue to receive an incredible value, especially those taking advantage of our 4G LTE network," AT&T said in a statement confirming the news.

Jackdaw Research analyst Jan Dawson (a FierceWireless contributor) said that AT&T in the third quarter reported that nearly 90 percent of its smartphone users were on usage-based plans -- meaning that around 6 million customers may still be on AT&T's unlimited data plans. AT&T didn't immediately respond to a question on the topic.

On its website, AT&T explained that users can switch from its unlimited plan to its newer plans, but can't switch back to the unlimited plan. The carrier added that it would waive any applicable early termination fees for customers who decide to cancel their AT&T service due to the $5 per month price increase.

AT&T discontinued offering its unlimited data service to new customers in 2010. The company replaced the offering with a tiered pricing model that it continues to offer today. AT&T launched its tiered pricing in 2010 with options ranging from 200 MB of data for $15 per month to 2 GB of data for $25 per month. Today the carrier offers shared data plans ranging from 300 MB for $20 to 15 GB for $100.

AT&T isn't the only carrier to increase the price of its unlimited data service for those customers who still subscribe to the offering. In recent weeks, Verizon (NYSE: VZ) too increased the price of its unlimited data plans by $20 per month for the customers who still have grandfathered unlimited plans. Verizon said in October that just 1 percent of its customers are still on its unlimited data plans. Verizon discontinued its own unlimited data offer to new customers in 2011.

Both T-Mobile US (NYSE:TMUS) and Sprint (NYSE: S) still offer unlimited data services, though both carriers recently increased their pricing for those options. T-Mobile in recent weeks said it would increase the price of its unlimited data offering from $80 per month to $95 per month for an individual, and Sprint increased the price of its individual unlimited data service by $10 per month, to $70 per month, in October.

AT&T's price hike on its unlimited data plan isn't the first time the carrier has tweaked the offering since discontinuing it for new customers. For example, in September AT&T increased the amount of data customers on its legacy unlimited data plans could burn through before they see their speeds throttled. Previously, the upper limit was 5 GB but the carrier increased that threshold to 22 GB.

For more:

- see this 9to5Mac article

Related articles:

Verizon to hike prices for grandfathered unlimited data plan users by $20/month

AT&T now lets customers with unlimited data plans use 22 GB before throttling them

AT&T kills unlimited data pricing, supports iPhone tethering