T-Mobile USA will stop selling its older and cheaper limited-data plans to postpaid customers, shifting entirely to its new "unlimited" data plans that impose bandwidth limits on video and tethering unless customers pay extra. To ease the transition, T-Mobile will offer bill credits of $10 a month to customers when they use less than 2GB per month.

T-Mobile began its shift to unlimited data plans in August with the introduction of T-Mobile One, which starts at $70 a month. While there are no data caps, customers have to pay a total of $95 a month to get high-definition video and mobile hotspot speeds of greater than 512kbps.

The carrier said in August that the unlimited plan would be "replacing all our rate plans," including its cheaper plans that cost $50 or $65 a month. Nonetheless, T-Mobile kept selling limited postpaid data plans to new customers for a few months, but yesterday CEO John Legere said that as of January 22, T-Mobile One will be the "only postpaid consumer plan we sell."

Existing postpaid customers can keep their current plans. For new customers, T-Mobile will presumably keep selling its prepaid plans that cost $40 to $60 a month and come with 3GB to 10GB of data.

T-Mobile also said yesterday that it will start including taxes and fees in its advertised rate when customers sign up for new T-Mobile One plans and enroll in automatic payments, essentially giving subscribers a discount. "The average monthly bill for a family of four will drop from $180.48 to $160, according to a company spokesman," The Wall Street Journal reported.

This perk is just for T-Mobile One, so it isn't available for customers on prepaid plans or any of the older postpaid plans with monthly data limits. T-Mobile also isn't automatically applying the tax and fee benefit to existing postpaid customers even if they already have T-Mobile One and are enrolled in autopay. "You are not automatically enrolled," T-Mobile says. " We think everyone will want to switch but at T-Mobile customers always have the choice. You can preregister for this new feature here to get your taxes and fees included effective with your February charges."

Existing customers also have to opt in to the new "KickBack" program in order to qualify for $10 monthly credits when they use less than 2GB a month. Customers can opt into this program beginning January 22. "KickBack pays you back for data you don’t use," T-Mobile said. "If your total monthly data usage on any line (on device & tethering) is 2GB or less and you pay on time, we will credit you up to $10 per line on your next bill."

The $10 credit can be applied to each line on an account. If the line price is less than $10, the KickBack "would bring your net line price down to $0," but "If you’re on a plan where taxes aren’t included, you’d still pay taxes and fees."