The major carriers are following the voluntary guidelines that were first laid down in 2005, but on many smaller issues they had written their own rules, said MMA President and CEO Mike Wehrs. These range from the wording of disclosures to policies established because of legal settlements, he said.

"They differed on dozens and dozens of points," Wehrs said. For example, where one carrier would require advertisers of texting services to advise consumers that "standard messaging rates may apply," another would demand the wording, "standard data rates may apply." Although most subscribers wouldn't notice the difference, each carrier has had to maintain an expensive auditing and enforcement operation to make sure its rules were being followed. The accord announced Monday will eliminate as much as 85 percent of those differences among carriers, Wehrs said.

The accord is another step toward helping consumers trust mobile advertising and overcoming its association with bait-and-switch problems from a few years ago, said Mark Donovan, an analyst at ComScore M:Metrics.

Inconsistency is one thing that makes it harder for advertising companies to work with carriers, said Manik Khanna, an associate in advertising strategy and operations at Amobee, which helps mobile operators sell advertising with all forms of media they control.

"This is just one step in 100 steps that the carriers need to take," Khanna said. Overall, they need to recognize the potential for revenue in advertising linked to applications, mobile Web pages, games, ringback tones and other forms of media, he said. For example, there is a huge revenue potential for advertising in text messaging, where most messages that consumers send use only one-third or less of the 160 characters allotted, Khanna said.