AT&T yesterday began offering “double the data for the same price” to new customers and existing customers who sign new contracts, apparently forgetting that its network is so congested that speeds must be throttled when people use too much data.

Like other carriers, AT&T slows the speeds of certain users when the network is congested. Such network management is a necessary evil that can benefit the majority of customers when used to ensure that everyone can connect to the network. But as Federal Communications Commission Chairman Tom Wheeler has argued, the carriers’ selective enforcement of throttling shows that it can also be used to boost revenue by pushing subscribers onto pricier plans.

AT&T’s throttling only applies to users with “legacy unlimited data plans,” the kinds of customers that AT&T wants to push onto limited plans with overage charges. Initially, the throttling was enforced once users passed 3GB or 5GB in a month regardless of whether the network was congested. In July, AT&T changed its policy so that throttling only hits those users at times and in places when the network is actually congested, according to an AT&T spokesperson. (UPDATE: It turns out LTE is still being throttled regardless of whether the network is congested. The change was only for 3G and HSPA.)

You can use the Internet Archive’s WayBack Machine to see that, through June, AT&T throttled all unlimited subscribers whether its network was congested or not. The site, both then and now, encourages heavy data users to switch to a tiered or shared data plan. AT&T says that more than 80 percent of its postpaid smartphone subscribers are on limited plans.

AT&T's throttling hits “unlimited” customers even when they use less data than subscribers on limited plans. New AT&T customers who buy ”Mobile Share Value” plans can normally get 15GB to 50GB of data per month for two to 10 lines. But under the new promotion, similar to one launched by Sprint, AT&T is doubling that to 30GB to 100GB at the same price for new customers who sign up by the end of October. The doubled data remains on subscribers’ accounts until they sign a new contract.

At the lowest price, this can work out to as little as 3GB per user when customers share 30GB across 10 lines, or 15GB per user for customers who share the same 30GB across two lines. At 100GB shared, each user gets anywhere from 10GB to 50GB depending on how many lines the data is spread across.

This isn’t to say that the deal isn’t a good one, relatively speaking. If you were planning to sign up with AT&T anyway, you might as well do it during a promotion that offers more data at the same price.

But AT&T’s ability to give far more unthrottled data to new subscribers than it provides to its longest-standing customers, the ones who specifically pay for unlimited data, illustrates how arbitrary the limits are. (AT&T may throttle limited users on congested cell sites for all we know, but the company’s official line is that only unlimited users are throttled.)

One commenter on a DSLReports story today did a good job summing up AT&T’s congestion management policies:

You see, when you use data on a Grandfathered Unlimited Data Plan, that's called "congestion," so you're throttled at 5GB to EDGE-like speeds to "prevent" it. Note this "congestion" doesn't occur when you double a shared 15GB data plan to 30GB, or a 20GB plan to 40GB, or a 30GB plan to 60GB, or a 40GB plan to 80GB, or a 50GB plan to 100GB. It doesn't occur if you let both new and current customers keep this "doubled data" in perpetuity, or at least until they change their plan. No, "congestion" only happens with Unlimited Data Plans throttled at 5 GB. What a farce.

FCC scrutinizes all major carriers

Verizon Wireless announced in July that it would begin throttling unlimited data users with LTE devices, just as it already did with 3G users. In response, Wheeler demanded that Verizon provide a “rationale for treating customers differently based on the type of data plan to which they subscribe, rather than network architecture or technological factors.”

Verizon responded that the policy is necessary to give users on unlimited plans an “incentive to limit usage.” Customers who have limited plans and face overage charges if they go over the limits already have such incentives, carriers say.

Verizon also pointed out that its policy is similar to those implemented by other carriers, but Wheeler didn’t buy that argument.

"'All the kids do it' was never something that worked for me when I was growing up," Wheeler said after an FCC meeting in August, Reuters reported.

Wheeler said he was looking into all the carriers’ throttling practices but hasn’t yet said if he will propose new rules on data throttling.