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The lawsuit alleges the company -- Cheap2Dial Telephone LLC -- charged more than 2,500 people since 2008 using a practice called "cramming." Swanson said the unwanted charges are hard to identify, and may show up in small amounts that accrue unnoticed over time.
"These charges are designed to fly under the radar. They are small enough in amount that a lot of people don't detect them," Swanson said. "They are buried on the bill; they are put under names like billing services or long distance services, things that a lot of people wouldn't catch."
Swanson said a lot of people pay online or through auto pay and often don't even look at the charges.
"The bottom line is that people don't realize that their phone bill can be a credit card," she said.
U.S. Sen. Amy Klobuchar said the Senate Commerce Committee is also investigating telephone companies over their role in billing for the charges.
Klobuchar also said that the unwanted charges are often hard to identify.
"Sometimes it's just $2.99 or something and it literally goes on for years and years until someone finally notices it," Klobuchar said. "So there is a major investigation actually going on with the commerce committee as well as with the FTC."
Cheap2Dial did not immediately respond to a request for comment.