James Martin/CNET

Those of you new to T-Mobile will be out of luck if you're hoping to walk into a T-Mobile store and walk out with a tablet and 200 megabytes of free data without putting any money down.

After promising to fix an "executional mistake" that forced new customers to sign up for a $10 On Demand plan, T-Mobile clarified to CNET that new customers who want to take advantage of T-Mobile's no-money-down plan are required to sign up for a $20-a-month plan.

Unlike the On Demand plan, which was simply a fee for staying on T-Mobile's network, the $20 plan does provide for an additional 500MB of data at its 4G LTE speed. The 200MB of data is "free," but doesn't kick in until after you sign up.

Existing T-Mobile customers with a phone plan can access the 200MB of free data without signing up for additional plans. New customers who paid full price for their iPad Air or any other tablet will be able to get the 200MB data plan for free. Or customers can bring in their own T-Mobile-compatible tablets.

T-Mobile marketing executive Andrew Sherrard confirmed the policy to CNET on Sunday. He noted that not every person qualifies for the equipment installer plan, and that even individuals wanting a smartphone under such a plan have to pass a credit check. He said the company is working to make matters clearer in its communication on its Web site and with its sales staff.

"As we roll into this new market, things have been a little bumpy," Sherrard conceded. "It's not as smooth as we would want it to have been."

The launch of the iPad Air and T-Mobile's free tablet data plan was supposed to ignite the carrier's push into the tablet business, an area where it hasn't been particularly strong. Even as the company has managed to turn its phone business around, larger rivals such as AT&T and Verizon Wireless have grown their tablet customers.

But the bungled launch, which Sherrard said included a legacy policy that forced new customers to sign up for a $10 monthly fee, has been a black eye for a company that has made a lot of noise about exposing the duplicitous actions of the wireless carriers.

"We're working around the clock to get this fixed," he said.

The free data plan and monthly installment model was supposed to be a hook to customers on other carriers, giving them reason to reconsider T-Mobile. But the requirement to either pay the full price for the tablet or sign up for a plan may turn off some customers.

Sherrard said T-Mobile was seeing strong early demand.

"We still think it's an incredible offer," he said. "As we go forward, we'll work on the execution issues."

Clarification at 7:43 p.m. PT: Story updated to focus on the requirement to sign up for a $20 plan for customers wanting to pay for the tablet in monthly installments.