Swanson said she had received hundreds of complaints from Minnesota residents, including some who said they were threatened with a $200 cancellation fee for trying to get out of contracts they thought had expired.
"The company has used hidden trip wires to trap unwary consumers into lengthy contracts simply because they made small changes in their plan," Swanson said.
She said Sprint, based in Reston, Va., with operational headquarters in Overland Park, Kan., violated state laws that require consumers receive enough information and give knowing consent before contract terms are altered. She said she did not coordinate her action with officials in other states.
Some Sprint customers who accepted a "courtesy discount" were unwittingly agreeing to stay with the company longer, according to court papers. Others had contracts extended when they added more minutes to their plans, even though they received assurances the change wouldn't affect their contracts' length.
Swanson said she is investigating complaints against other wireless companies, but she declined to say which. She decided to sue Sprint first because it was cited most often by angry constituents, she said.
She is seeking restitution for victims and wants the court to penalize Sprint up to $25,000 per incident.
Sprint spokesman John Taylor said company attorneys were reviewing the lawsuit and could not comment.
"It is Sprint Nextel's policy to go over the contract with the customer so they understand all aspects of it" before it is agreed to "or before the customer initiated changes are made to their account," he said.
Taylor said the company sends written confirmation of all account updates and allows customers who change their minds to opt out.
Swanson announced her lawsuit, filed in Hennepin County District Court, at a state Capitol news conference where she was surrounded by people who felt duped by the company.
Among them was certified financial planner David Peterson of Andover, who said he received a letter in July thanking him for extending his contract on four phones. When he called to question the action, he said he learned from a customer service agent that his contract was lengthened for apparently inquiring about a plan discount — something he denies took place.
Peterson said he was able to reverse the charges, but only after he and his wife spent hours dealing with the company.
"I was livid at the way they handled this. They've treated us extremely poorly," Peterson said.