A growing number of customers on AT&T’s unlimited data plan are complaining about the company’s throttling of their usage.

AT&T no longer offers an unlimited data plan to shoppers. But they used to, and those that were on it remain grandfathered into that plan unless they choose another one.

Current AT&T data plans for smart phones are $20/month for 300 MB, $30/month for 3 GB, or $50/month for 5 GB. For tablets, the plans are $14.99/month for 250 MB, $30 to $35/month for 3 GB, and $50/month for 5 GB. There are various restrictions and requirements for each plan.

AT&T eliminated its unlimited plan in the summer of 2010, Those that were on it were grandfathered in. Users who have kept it pay $30/month.

In October, 2011, AT&T changed its policies and began limiting the ‘unlimited’ plan. At the time, AT&T minimized the effects of the change, saying it would only affect the top 5% of its heaviest data users.

When the policy was changed, AT&T declined to say what the throttling point would be. They’ve continued to remain silent on that issue. They will say that users will receive alerts when nearing the throttling point, and once reached, the high-speed data connection will be slowed until the following billing cycle.

Users of AT&T’s unlimited plan are complaining that while they’re paying the same amount that users of the 3 GB plan are paying, they begin getting throttled back long before they reach that amount. In essence, they’re able to use less with their unlimited plan than those paying for the 3 GB plan.

On AT&T’s own user forum, recent comments include:

“Very disappointed about speed being reduced to .03 Kbps after only 2 gb of data usage.”

“Is it true at&t is now throttling all unlimited data plans after 2gb trying to get users to drop there unlimited plan?”

“I’m also extremely upset about this whole throttling business.  I have 2.1Gig of use in Sacramento!  Highly unlikely I’m in the top 5% for data use.  If this doesn’t get resolved ATT is pushing us to find a different service.”

“With all of the tablets and smart phone users out there, I find it very hard to believe that only 5% of users use over 2Gb of data! Prove it!!!”

“I called to officially complain and to let them know I have also filed complaints with the FCC and the FTC. They’ll tell you till their blue in the face that what they are doing is perfectly legal and justified.”

“Today, I find out that my data is being throttled when my total data usage this month is only 1.5Gb.  Where is the unlimited in this? ”

“Just filed a complaint with the BBB. Hope all of these complaints triggers ATT to do the right thing in order to keep their client base otherwise other competitor client bases will grow.”

Some forum poster’s say that when they called to complain about the throttling, AT&T customer service steers them toward signing up for a current tiered plans. Others have said they’ve been told by customer service that the plan is still unlimited, because data is not cut off, it’s only slowed.

According to a story in The Post and Courier, it’s some pretty serious slowing. One customer they profiled had his internet speed reduced to 1% of what was normal.

AT&T has not made any statements concerning the growing number of complaints. We will let you know if they do.