DETROIT ? SBC Communications – the former Southwestern Bell Company spun out in 1984 by AT&T when Ma Bell was broken up by the federal government ? is again known as AT&T. SBC closed the books Friday on its $16.9 billion acquisition of the former American Telephone & Telegraph Company and adopted its former parent company?s name.

SBC acquired the former Ameritech Corp, which, in turn, had absorbed Michigan Bell. The new SBC now AT&T received final regulatory approval from the state of California on Friday. The Federal Communications Commission and the U.S Department of Justice gave their approval of the merger last month with only a few minor conditions.

The acquisition was announced in January and originally wasn’t expected to close until early 2006.

The merger is a pivotal event in the history of the telecommunications market. Twenty-one years after federal regulators forced the old AT&T to split up, Ma Bell has come full circle.

After the split, AT&T became a long-distance phone company. Its local phone business was split among several Baby Bells, one of which eventually became SBC.

Now the two sides of the business have been reunited, but under a much different set of circumstances.

“This merger of SBC and AT&T, and the coming merger of Verizon with MCI, are big, big news in the telecom industry,” said Jeff Kagan, a telecommunications industry analyst, told CNET.Com.

“We have watched the industry change over the last 10 to 15 years,? Kagan said. ?In 1996, the Telecom Act spelled out the rules of competition between the local and long-distance telephone companies. The local companies have won that war and are acquiring the long-distance giants.?

The past decade has seen tremendous change in the telecommunications industry, from a regulatory as well as a technology perspective.

The Telecommunications Act of 1996 and the ensuing regulatory battles that have followed have shaped the landscape for new competition in the telephone and high-speed Internet access markets.

The adoption of cell phones and the emergence of new technologies such as voice over Internet Protocol, have also had an impact on the industry. These changes caused commoditization of long-distance telephony and ultimately led to the market consolidation trend.

Through its subsidiaries and affiliates, AT&T is considered the largest telecommunications company in the United States. It boasts the largest number of DSL lines in the country and has the largest long-distance network.

With these assets, the company will continue to compete head-to-head with cable operators, not just in the telephony market but also in high-speed Internet access and TV.