The fine is the highest ever imposed by the FCC, according to FCC Chairman Michael Powell.
The regulator had made sharing a condition of the San Antonio-based telecom carrier's 1999 merger with Ameritech. But SBC "willfully and repeatedly" denied access, the FCC said in a statement Wednesday.
The nation's second largest landline carrier instead forced competitors to spend time and money filing lawsuits seeking the access, the FCC said.
"SBC...went out and broke the (requirements) in five different states," Powell said in a statement. "Such unlawful, anti-competitive behavior is unacceptable."
"Instead of sharing, as the law requires, SBC withheld and litigated, forcing competitors to expend valuable time and resources to exercise their rights under the FCC's order," Powell added.
An SBC representative was not immediately available for comment.