AT&T has returned fire in a price war with T-Mobile designed to keep its customers and attract new ones.

AT&T Mobility has cut $40-100 a month off the price of plans targeting some of its most lucrative customers — families with multiple phone sharing a lot of data.

Under its newest offer announced Saturday, a family with four smartphones sharing a 10GB data allowance will see their bill cut from $200 to $160 a month effectively immediately. Any family plan customer with 10GB or higher usage allowances will also see their bill cut by $40-100 a month.

The price cut comes in response to fierce competition from T-Mobile, which has repeatedly bashed AT&T in its advertising campaigns. Now a customer with three smartphones will find AT&T’s new plan price just $5 more than what T-Mobile charges, although T-Mobile’s offer includes unlimited data.

“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.

AT&T is also offering a $100 bill credit for each new line added or for activating each new tablet, mobile hotspot, or AT&T’s wireless home phone service until March 31.

The contrast in pricing between AT&T, hounded by T-Mobile, and Verizon Wireless, which has largely ignored the price war, is striking. Verizon Wireless charges up to $125 more a month for its family plans with identical data allowances and features.

The new offer requires no contract, and phones must be purchased at full price either up front or in installments. Existing, on-contract customers with subsidized phones will pay more.

AT&T has also stepped up customer retention efforts, handing out hundreds of dollars in service credits to some threatening to leave for T-Mobile.

Customers are receiving an average of $55 a month in service credits over the next year by tweeting complaints to AT&T’s social media team: @ATTCustomerCare and @ATT

Those on family share plans with several lines of service complaining that AT&T is charging too much and are planning to switch to T-Mobile are being offered discounts such as $70 a month in service credits for the first six months and $40 a month for the next six months after speaking to an AT&T representative arranged through Twitter.

Customers get a less charitable response in AT&T stores where some employees have dared customers to switch to T-Mobile claiming they will be unhappy with the slow data service and coverage areas. In short, no service credits or retention offers are available from in-store representatives. Customers must appeal to AT&T’s social media team to get a discount.

[flv]http://www.phillipdampier.com/video/ATT New Mobile Share Value Plan for Families 2-1-14.mp4[/flv]

AT&T explains the new pricing for their Family Share plans. (1:27)