WASHINGTON — It’s been dubbed cell phone "bill shock," and it’s clear why: A woman returning from Haiti after the earthquake disaster is greeted with nearly $35,000 in text messaging charges. An Orange County, Calif., man is socked with a $3,300 bill after checking e-mail on his smartphone during a cruise celebrating his wife’s recovery from breast cancer.

Even Apple co-founder Steve Wozniak experienced it last year, unwittingly ringing up $7,000 in roaming fees on his iPhone during a three-hour drive through Germany’s countryside.

"What are you talking about?!" Wozniak said when he learned of the charges from AT&T.

Those anecdotes are extreme, but according to the Federal Communications Commission, one in six cell phone users has endured "bill shock" of some magnitude. And the bill is often a whopper when it happens: $100 or more for two-thirds of those who complained to the FCC in the first half of this year, and upward of $1,000 for 20 percent of that group.

Now the federal agency is poised to step in with new rules to help customers avoid unexpected bills after exceeding their usage limits. Cell phone companies are crying foul, saying they already offer customers tools to monitor their voice minutes and texts, and that regulators shouldn’t dictate how they provide service.

"I do think consumers have a certain amount of personal responsibility to understand what service and what offerings they’ve signed up for," said John Walls, a vice president at CTIA-The Wireless Association, a trade group. "Just like you and I need to know what kind of gas to put in your car, and if there are any questions you look at the manual, all those tools are available now" for cell phone users. He also said he doubts that "bill shock" is as widespread as the FCC says.

The proposed rules, which could be approved early next year, would require wireless carriers to send customers a voice or text alert when they are about to exceed their voice, data or text limits. A similar warning would come when a user is about to incur hefty international roaming charges.

That’s what happened to Wozniak during a trip to Germany last year for a "Segway Polo" tournament. The Apple legend was hit with $7,000 in roaming charges, even though he had signed up for a generous international usage plan.

AT&T quickly reversed the charge, admitting a mistake. "I think they would’ve dealt nicely with anyone," Wozniak said in an interview last week.

But others have had to haggle for months to try to get charges reversed, and they’re not always successful. Kerfye Pierre returned home from Haiti in February after visiting her sister and helping with the relief effort. A T-Mobile representative had told her the carrier was extending courtesy cell phone usage to customers in the disaster-stricken country. But the offer didn’t extend to texts and data, which Pierre used to communicate with family back home because cell service was poor.

The tab? $34,782. Pierre couldn’t believe it. "I tried to get them to see it was an emergency," she said.

The FCC stepped in to help Pierre, and T-Mobile forgave most of the charges. But as of last week, the carrier still said she owes $4,435, according to an agency official. A T-Mobile representative said the company’s privacy policy prohibited her from commenting on individual customer accounts.

Richard Barbazette of Orange County had better luck with T-Mobile after using his smartphone to check e-mail during a trans-Atlantic cruise with his wife. About a week into the trip, a fellow traveler suggested that he and his wife, who were celebrating her recovery from breast cancer, make sure they weren’t accruing international roaming charges. In fact they were, to the tune of $3,336.

After about five months of back and forth, T-Mobile forgave the fees, but only after a consumer group threatened to file a complaint with state regulators.

"It was not a fun experience," Barbazette said. "They have an arrogant attitude."

The T-Mobile spokeswoman said that customers can use a shortcut number to get updates on their call minutes, and that the company offers an "occasional use" data plan that shuts off after users reach $50 a month in charges.

Verizon goes further, sending a text message to users "trending toward exceeding" their voice, data or text limits, a spokeswoman said.

But tools for avoiding exorbitant overage fees vary by carrier, FCC officials say.

"It’s true that different carriers are taking steps in this direction," said Joel Gurin, chief of the agency’s consumer and governmental affairs bureau. "But there’s not a level of consistency that consumers can count on, and we believe there should be."