Cellphone companies promised Monday to warn subscribers before they go over their monthly limits for calling minutes, text messages and data use.

The pledge comes in response to a threat of regulation by the Federal Communications Commission, which wants to curb nasty surprises in the monthly bills of wireless subscribers.

CTIA -- The Wireless Association, a trade group representing the major cellphone companies, said they're also promising to warn subscribers that they're paying roaming fees if they travel abroad.

The warnings will arrive as text messages, and subscribers won't need to sign up for them -- they'll arrive automatically. CTIA said its members will have warnings in place on at least half their plans in a year and on all of them in two years.

AT&T Inc. and Verizon Wireless, the two largest carriers, already provide text-message warnings on their data plans but not on text messaging or calls. Instead, subscribers have to look up their usage data.

The announcement was made jointly by the CTIA and the FCC, which credited Consumer's Union, the publisher of Consumer Reports, for raising awareness of the issue. The magazine had found that many of its subscribers had been startled by high monthly bills.

Curbing occasional high bills is unlikely to have much of a financial effect at phone companies. Analyst Michael McCormack at Nomura Securities noted that the companies say that only a few percent of their subscribers exceed their allotments in a month. The trend over the past few years of making calls to other cellphones "free," or not counting toward the plan limits, has reduced the number of people who go over on calling minutes, he said.

Phone companies are also moving away from charging for each text message or selling "buckets" of 500 messages per month. Rather, they have moved toward offering unlimited text messaging.

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