AT&T has ended negotiations to buy a one-third stake in Olimpia, a holding company that owns about 18 percent of Telecom Italia SpA’s ordinary shares.AT&T, in a statement released Monday, said it appreciated the opportunity to explore a possible investment in Olimpia and Telecom Italia, but it has decided not to pursue the matter further. AT&T, which announced negotiations in early April, did not give a reason for the withdrawal.Concerns in Italy about foreign ownership of Telecom Italia appear to have scuttled the AT&T deal, said Mike Cansfield, a telecom analyst for Ovum. Unions have protested the deal. Technology Industry