Weis, 53, was assigned as acting chief executive when his predecessor, David Dorman, left the post last month to become president of AT&T, the company said in a statement. Concert is a joint venture between AT&T and British Telecom.
Previously, Weis was senior vice president of AT&T's Business Services Global Operations unit, an Internet network serving more than 30,000 businesses. He took the position in April 1999 after the telecommunications giant purchased the IBM Global Network.
Based in New York, Concert provides telecommunication services to large corporations, other carriers and Internet service providers.