ATT Inc, the No. 2 U.S. mobile provider, had slower wireless subscriber growth in the latest quarter than Wall Street had estimated, sending its shares down 1.6 percent in late trade. ATT also added fewer subscribers in the latest quarter than two big rivals, Verizon Wireless and T-Mobile US. Investors have been worried that ATT could become embroiled in a mobile price war. No. 4 U.S. mobile service T-Mobile US has spent months directly marketing to ATT customers while ATT recently offered to pay T-Mobile customers to switch.