AT&T Co yesterday stepped up its involvement in telecommunications equipment manufacture in Europe with the acqusition for $80m of Polish telephone equipment manufacturer Telfa SA, one of the biggest foreign investments in Poland since it ended Communist rule in 1989. AT&T Network Systems International, which has 10% of Italtel SpA in Italy, signed to pay $28m for an 80% stake in Telfa from the northwestern city of Bydgoszcz, and will also invest $45m in the next six years and increase its own capital in Telfa by $7.2m before June. AT&T plans to assemble its 5ESS digital telephone exchanges and transmission equipment in Poland.