* US Justice Dept has sued to stop buy of T-Mobile USAWASHINGTON, Oct 13 (Reuters) - A federal telecommunications regulator asked AT&T Inc on Thursday to provide data on claims that its deal to buy T-Mobile USA would mean a net gain of U.S. jobs, saying its responses on this issue “remain incomplete.”The Federal Communications Commission said in a letter to AT&T’s lead attorney Rick Rosen that the agency had asked about U.S. jobs in a request for information sent in May.AT&T has defended the $39 billion transaction, saying it would bring 5,000 overseas jobs back to the United States, but the FCC pressed for data to show there would be a net increase in U.S. jobs.”Our review of the information currently in our record suggests that AT&T’s response on this issue remain incomplete,” wrote Rick Kaplan, chief of the FCC’s wireless communications bureau.Kaplan also asked for all AT&T data on the “size and location” of AT&T’s workforce currently and after the planned merger is consummated. The $39 billion deal would merge two of the four large national cellphone carriers.In August, the Justice Department sued to stop the deal, saying that the transaction would lead to higher wireless prices. A trial will begin on Feb. 13.The FCC must also approve the merger for it to go ahead.Last month, attorneys general from California, Illinois, Massachusetts, New York, Ohio, Pennsylvania and Washington signed onto the effort to stopThe deal would vault AT&T over Verizon Wireless, a venture of Verizon Communications and Vodafone Group Plc , into the No. 1 spot. T-Mobile USA is now owned by Deutsche Telekom AG .Sprint , the third-largest carrier, has bitterly opposed the AT&T buy.A key government concern is that T-Mobile, the No. 4 wireless carrier, generally costs less than other carriers so its disappearance could mean higher prices for wireless service.