AT&T is rolling out cheaper monthly plans starting Sunday that will allow customers to bring their own smartphones and pay $15 less on their monthly bills.

AT&T is adding new monthly plans with 'No Annual Service Contract' options for new customers who bring their own smartphone and to existing subscribers who are coming off their contracts. The latest move follows increasing pressure from its rival T-Mobile, whose cheaper rates have been a major attraction. AT&T will start rolling out its new "Mobile Share Value" plans starting Sunday, December 8.

The new plans will reduce the monthly subscriber bills by $15 for people who bring their own phone. These savings can also be availed by customers purchasing a new smartphone with no down payment under the carrier's Next plan, and those who are no longer in contract with AT&T.

Under the new plans, customers will pay for data and a separate fee for each device attached to the plan. The price of adding a new smartphone, which previously depended on the amount of data, will be $40 a month for a subsidized phone under a contract and $25 if customers pay the price of the smartphone. Subscribers can also opt for higher data plan by paying extra, which will cost them $55 for 2GB instead of 300MB and $100 for 10GB.

"With our new Mobile Share Value Plans, customers don't have to compromise," David Christopher, chief marketing officer, AT&T Mobility, said in a press release.  "Our new no contract option lets customers add a smartphone to the nation's fastest and most reliable 4G LTE network at a lower monthly cost.  Customers want great value and a premium network - and now they can save more and get unlimited talk, text and data to share."

AT&T has been criticized for charging double with its Next plan, which breaks the actual cost of the smartphone into monthly installments and allows frequent upgrades. But the deal turned out to be an overpaying tragedy for those who do not upgrade their phones, as the subsidy charge would not go away after the full cost of the phone is paid off.

With the latest offerings, AT&T wants to give the customers an option to save $15 a month once the existing customers are out of a contract.