Cellphone users may want to think before ignoring unknown phone numbers; it might be their wireless carrier saving them money.

Wireless cellphone companies have agreed to send warning alerts to customers before billing them for unexpected charges, Julius Genachowski, Federal Communications Commission (FCC) chairman, said early last week.

Genachowski said CTIA, the International Association for the Wireless Telecommunications Industry, will ensure wireless companies alert users before hitting them with overage or roaming charges, a practice called bill shock.

“(Bill shock) is when wireless subscribers experience a sudden, unexpected increase in their monthly bill,” Genachowski said in an Oct. 17 statement at the FCC Bill Shock Event. “This solution will give consumers the information they need to save money on their monthly wireless bill. These actions harness technology to empower consumers and ensure consumers get a fair shake, not bill shock.”

Wireless companies will send free and automatic voice or text alerts to consumers when they reach their monthly text, voice or data limits, or are about to incur international roaming charges.

Companies will also inform users of tools that let them set and monitor their own usage limits, but they’ll have to wait a little bit.

The plan, called Wireless Consumer Usage Notification Guidelines, will go into effect beginning Oct. 17, 2012. Consumers will receive at least two of four notifications by then, and receive all of them beginning April 17, 2013.

According to Consumer Reports magazine, one in five wireless users surveyed reported experiencing “bill shock.”

Philosophy major Josie Avendano switched wireless companies after receiving too many unexpected high bills from Nextel/Sprint, who he said didn’t warn him of overage charges.

“I was an aggravated customer,” he said, although Nextel/Sprint would usually reduce or subtract the extra charges after he called to complain.

Avendano now has Metro PCS after getting charged more than $100 extra on his wireless bill for going over his limit, and sometimes for things he said he didn’t even do.

Avendano has an unlimited plan with Metro PCS now and he does not get charged overage or extra usage fees. They don’t allow access to features that a person is not signed up for to avoid those extra, unknown charges, he said.

“I think it will be quite helpful to let people know before they do hit their boundaries,” Avendano said. “I wouldn’t mind a little reminder here and there.”

Although social work major Carla Ayala said she has only experienced bill shock once, Verizon didn’t warn her of roaming charges when she was in Mexico. She said her phone was still on, working and sending her e-mails, but when she returned home, she was charged an additional $10.

“I think it’s a good thing,” Ayala said, regarding the new alert plan. “We think (cell phones plans are) so liberal, and we have so many minutes but then you go over and can’t pay your bill.”

The FCC has withheld from making this implementation a regulation, but rather will take a “trust but verify” approach to ensure wireless companies comply with the agreement, Genachowski said.

“Consumers Union and the FCC will work together to launch a new web portal on the FCC website that will allow consumers and anyone to see what types of alerts are provided by each CTIA member,” Genachowski said. “This portal will allow the FCC and the public to track whether carriers have complied with their obligations.”