AT&T is trying to nudge customers on grandfathered unlimited data plans to switch to ones with limited data. But the company's latest move isn't all that punitive: AT&T is raising the price, but for the first time in seven years, and by only $5 a month.

The $30-per-month plan will cost $35 starting in February, AT&T announced. The change will affect a few million customers.

Compared to AT&T's years-long history of throttling customers on the old unlimited plans (which aren't offered to new customers), the price increase is pretty tame. It's also still cheap compared to Verizon, which recently raised its unlimited price from $30 to $50 a month. (The AT&T and Verizon prices don't include what customers pay for voice calls and text messaging, which can bring the total bill closer to the $80-100 range.)

But AT&T seems to expect some people to switch to limited plans because of the $5-per-month increase. The announcement reminded customers that "You can change your plan at any time," and encouraged them to learn about the "Benefits of Mobile Share Value" plans, which are limited and can cost more but include tethering and rollover data.

"Should you decide to cancel your wireless service because of the $5/mo. increase, we will waive the early termination fees (ETFs)," as long as customers cancel within 60 days after the price increase, AT&T also said.

Customers on device payment plans would still be responsible for paying off the entire device cost. Customers who want to switch carriers may need to ask AT&T to unlock their phones. Those who switch to a different plan but stay with AT&T will not be able to switch back to unlimited data in the future.

The remaining unlimited data customers often don't have contracts anymore, so AT&T could probably just force them onto limited data packages or raise the price even higher. Instead, the company has taken steps that might make holding onto unlimited data a hassle.

AT&T threatens to revoke unlimited data plans when it suspects that customers are tethering or sharing their phone's Internet connection with another device. We wrote about one man who said he was not tethering but received such a threat anyway.

AT&T also used to throttle unlimited data customers once they hit 5GB of usage in a month, slowing them down at all hours of the day and night until the billing cycle reset. AT&T finally changed the policy for all unlimited data users this year so that customers would only be throttled when the network is congested. AT&T also raised the throttle point from 5GB to 22GB. Now, customers can use 22GB without fear of throttling, but for the rest of the month they could be throttled if they connect to a congested tower.

AT&T's throttling of unlimited data drew a $100 million fine from the Federal Communications Commission and a lawsuit from the Federal Trade Commission, and the company is fighting both agencies to avoid having to pay the fine or refunds to customers. The FCC and FTC argue that AT&T deceived customers by marketing data plans as unlimited when in fact they were throttled to speeds that make using Internet services difficult or impossible.

AT&T has 57.7 million postpaid phone subscribers with smartphones, and nearly 90 percent of them are on usage-based data plans, instead of unlimited ones, AT&T said in a recent report to investors. That puts the total number of unlimited data customers at 5.77 million or so.

While AT&T and Verizon no longer offer unlimited data to new customers, T-Mobile and Sprint do. Sprint sells unlimited high-speed data with unlimited talking and texting for $70 a month. T-Mobile last month raised its unlimited plan's price from $80 to $95 per month, but existing customers can keep their previous rates for at least two years.