Remember when we told you to brace yourself because the death of unlimited wireless data in the United States is imminent? Well, the beginning of the end is finally upon us: Sprint, one of unlimited mobile data’s last and biggest and last defenders, will soon begin to throttle some wireless subscribers with unlimited data plans.

FierceWireless on Thursday reported that Sprint is “slamming the brakes” on unlimited high-speed data for around 5% of its wireless customers in congested areas. According to the report, postpaid Sprint customers and prepaid subscribers on Virgin Mobile or Boost Mobile will be throttled.

“[Throttling] will enable us to provide more customers with a high quality data experience during heavy usage times,” Sprint said in a statement to FierceWireless. “Once the customer is no longer connected to a congested cell site, or the site is no longer congested, speeds will return to normal.”

How do you know if you’re at risk of being throttled? According to the carrier, subscribers who use more than 5GB of data in a single billing period could experience slowed data speeds.

What constitutes a congested area? Whatever Sprint decides constitutes a congested area.

Of note, Sprint did say that subscribers will no longer be throttled once the leave congested areas.

Below is an example of a text message received by subscribers who might be at risk of having their data speeds throttled:

Beginning 6/1/14, to provide more customers with a high quality data experience during heavy usage times, Virgin Mobile USA may manage prioritization of access to network resources in congested areas for customers within the top 5 percent of data users.

Zach Epstein has worked in and around ICT for more than 15 years, first in marketing and business development with two private telcos, then as a writer and editor covering business news, consumer electronics and telecommunications. Zach’s work has been quoted by countless top news publications in the US and around the world. He was also recently named one of the world's top-10 “power mobile influencers” by Forbes, as well as one of Inc. Magazine's top-30 Internet of Things experts.