That's not true. AT&T was broken up around the same time British Telecom was privatized, both in the early 1980s. The difference was that British Telecom had been a government organ (part of the Post Office until 1981), while AT&T had always been a private corporation. When BT was privitized, the government had enormous latitude in imposing conditions on investors purchasing the assets. The U.S. government was not in a similar position. An antitrust violation doesn't give the government the right to just do whatever it wants with the company's assets.

The best course of action on the part of the U.S. likely would've been to permit the AT&T monopoly to continue. AT&T's regulatory treatment at the time permitted it to set prices to ensure a reasonable return on its capital investment. That had the effect of creating an enormous incentive on AT&T's part to invest a lot in its network (the more capital investment, the more profits). As a result, the U.S. telephone system was extremely high quality for its time.