Editor's note: Amy Gahran writes about mobile tech for CNN.com. She is a San Francisco Bay Area writer and media consultant whose blog, Contentious.com, explores how people communicate in the online age.
(CNN) -- If you like streaming lots of audio or video to your cell phone and you don't have an unlimited data plan, you might end up with a bad case of "bill shock" when your wireless carrier hits you with overage charges.
In October, under pressure from the Federal Communications Commission, U.S. carriers agreed to start alerting customers by text message when they're getting close to hitting their plan caps on data, phone minutes and text messages. This would allow users to either curb their use for the rest of the month or switch to a higher (and pricier) tier before they incur overage charges.
The carriers also agreed to fully implement these alerts within a year.
So, it's been six months. How are they doing?
Last week, the FCC started publishing updates on carriers' progress toward implementing these alerts.
Among the four major carriers, T-Mobile has gotten the most done: It's set up overage alerts for voice, data and international roaming plans. Verizon has implemented them only for data and international roaming. AT&T has alerts only for data plan overages and Sprint only for international roaming.
None of the minor U.S. wireless carriers has implemented any alerts, according to the FCC.
The FCC has promised to provide updates on the status of these efforts monthly.
An FCC survey conducted last year found that one in six mobile phone customers has experienced some degree of bill shock -- and nearly half of those had been surprised by bills that hit them with overage charges of $50 or more.