The nation’s two biggest local phone companies received approval Thursday from antitrust regulators to buy the two largest long-distance carriers in multibillion-dollar mergers that would change the landscape of the telecommunications industry.

The Justice Department cleared the mergers of SBC Communications Inc. with AT&T and of Verizon Communications Inc. with MCI Inc. without any significant conditions, such as the asset sales that critics said were needed to ensure adequate competition.

The Federal Communications Commission still must sign off on the mergers, and that could come as early as today when the agency meets for its monthly public meeting.

The SBC merger, valued at $16 billion, wouldn’t end the AT&T name. SBC, based in San Antonio, plans to change its corporate name to the iconic AT&T, company officials said.

New York-based Verizon would keep its corporate name after its $8.5 billion merger with MCI.