AT&T Inc., the second-largest U.S. wireless carrier is introducing service plans aimed at families that use lots of data, cutting $40 a month from premium users’ bills.

Under the new offer, families with four smartphones can pay $160 a month for 10-gigabits of shared data, unlimited calling and text messaging, the company said in a statement. A similar package under AT&T’s previous plan would cost $200, and Verizon Wireless charges $260 for the same plan. The offer requires no contract, and phones must be purchased at full price either up front or in installments.

The move is an escalation of competition in the mobile market where AT&T and T-Mobile US Inc. have run back-and-forth attack ads and offered $450 in credit to entice customers to switch service providers.

“This is about being competitive,” said David Christopher, chief marketing officer for AT&T Mobility. We feel we have the best network and the best value in the marketplace,” Christopher said.

T-Mobile, based in Bellevue, Washington, has gained 2.1 million monthly customers in the past three quarters. This is a reversal of its 2012 performance, fueled by a switch to no- contract plans and quicker phone upgrades and payment financing. The gains at T-Mobile have helped slow AT&T’s user growth. Earlier this week, the Dallas-based carrier said it signed up 566,000 contract wireless customers in the fourth quarter, compared with 780,000 a year ago.

All existing AT&T customers sharing 10-gigabits or higher will automatically be placed on the new plan, said Fletcher Cook, an AT&T spokesman. (Bloomberg)