Presumably, if Verizon, AT&T, Sprint or T-Mobile began to offer a campaign-donation text service, the other carriers would be forced into accepting campaign donations, analysts said.

Verizon and T-Mobile declined comment. AT&T representatives did not return requests for comment and CTIA spokeswoman Amy Storey declined to comment beyond saying that individual carriers "are still reviewing the FEC's advisory opinion."

Sprint spokeswoman Crystal Davis said that "while no formal agreements or decisions have been reached ..., we want to ensure this feature adheres to all federal and state campaign laws, protects the privacy of our customers, and ensures a seamless process for the carriers, mobile aggregators and donors."

'IT'S UNCHARTED TERRITORY'

In many ways, the FEC's unanimous vote on June 11 to approve text donations caught the wireless industry by surprise, the industry sources said.

The six-member FEC often deadlocks along party lines and in 2010, the agency rejected a similar donations-by-text proposal from the CTIA.

Last month's decision came in response to a request from political consulting firms Red Blue T LLC and ArmourMedia Inc and corporate aggregator m-Qube Inc, which processed millions of dollars that Americans texted to charities aimed at helping Haiti earthquake victims.

The proposal that the FEC approved last month was more specific than the failed 2010 plan in outlining how donations would make their way from a cell phone to campaign coffers while complying with legal limits and regulations.

The plan suggested that the aggregator would monitor donations and donors' phone numbers to try to make sure that the $200 limit for anonymous contributions was not exceeded.

But wireless carriers are "not just going to take the assurances" that an aggregator would monitor text donations effectively, said Jeffrey Silva, a telecommunications policy analyst at Medley Global Advisors. "They are responsible to shareholders, and the buck stops with them."

Besides seeking to avoid liability in determining donors' eligibility, wireless companies do not want to be blamed for allowing donors to exceed contribution limits.

Other questions that concern wireless carriers include whether the carriers should decide which campaigns should be allowed to use text donations, or whether carriers would be required to serve all campaigns, despite any risks to the carriers' reputations.

"It's uncharted territory and I imagine that lawyers at all these carriers are just looking at this from every single angle," Silva said. "Fundamentally, there's just so much more involved with political donations over charitable donations."

(Editing by David Lindsey and Xavier Briand)