A class action lawsuit filed in California says that T-Mobile markets certain phone plans as offering unlimited data, but then caps data use once consumers are locked into a contract.

The suit, brought in Superior Court in Yolo County, says that advertisements for T-Mobile's Unlimited Web & E-mail plans, offered for both Blackberry and other brands of smartphones, promise the consumer access to an unlimited amount of data. The plans offer a discount on new phones if consumers agree to sign a contract.

Trent Alvarez, the suit's lead plaintiff, bought two smartphones last year, and signed a two-year contract for each. The sales representative who sold the plans to him expressly represented that the data plan [Alvarez] was to receive would be 'unlimited,' according to the suit.

But in May 2010, Alvarez received a text message informing him that, Your data usage in this billing cycle has exceeded 10GB; Data throughput [speed] for the remainder of the cycle may be reduced to 50kbps or less. Alvarez called T-Mobile to have the volume and speed limits removed, but a representative refused his request.

According to the suit, the limits render Alvarez's phones essentially useless for anything other than making or receiving phone calls and text messages.

Little warning to consumers

Alvarez's experience is typical, the suit says, of consumers who are likely to be mislead by T-Mobile's promise of 'unlimited' data.

The only warning given to consumers, according to the suit, is a statement on the very last page of [a T-Mobile] brochure, buried in minuscule type barely readable, [that] 'Your data session may be slowed, suspended, terminated, or restricted if you use your service in a way that interferes with or impacts our network or ability to provide quality service to other users '

T-Mobile isn't the first carrier to be accused of falsely advertising data plans as unlimited. In 2007, Verizon settled a suit brought by New York Attorney General Andrew Cuomo alleging that that carrier placed invisible limits on its plans that purported to offer unlimited data capabilities.

This settlement sends a message to companies large and small answering the growing consumer demand for wireless services. When consumers are promised an unlimited service, they do not expect the promise to be broken by hidden limitations, Cuomo said of the settlement, which required Verizon to pay $1 million to consumers whose accounts were terminated after they exceeded the undisclosed limits.

If Alvarez's suit is to be believed, T-Mobile's line was busy when that message came through.

The suit requests restitution for money consumers spent on smartphones and the accompanying plans and an injunction prohibiting further misleading advertising.