The data overcharging claims in the study are timely because both Verizon Wireless and AT&T recently instituted data sharing plans that impose several tiers of shared data with a monthly cost. Both plans have an overcharge fee of $15 a gigabyte over the monthly limit.
Asked to comment on the study, a Verizon spokesman said the study appears to have examined only carriers using GSM networks, not CDMA, such as Verizon.
Verizon did not participate in the study, the spokesman said.
"I can tell you that Verizon Wireless is vigilant in these matters [raised in the study]," said Verizon spokesman Tom Pica. "We regularly monitor and audit our billing systems to ensure fairness and accuracy."
AT&T, which runs a 3G GSM network and is building a 4G LTE network, declined to comment on the study.
The CTIA wireless association, which represents all the major carriers in the U.S. and some from abroad did not respond to a request for comment.
Sprint, the nation's third largest carrier, touted its unlimited data plans for its wireless customers on the Sprint network in response to the UCLA study.
Data pricing from Sprint's competitors "is already complex, driving customer worries about incurring data overage," a Sprint spokesman said. Using unlimited data on the Sprint network "eliminates the worry of any data overage charges."
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