President Donald Trump's personal lawyer Michael Cohen leaves federal court in the Manhattan borough of New York City, New York, U.S., April 16, 2018. Lucas Jackson | Reuters

"Our company has been in the headlines for all the wrong reasons these last few days and our reputation has been damaged," said CEO in the message to employees. "There is no other way to say it – AT&T hiring Michael Cohen as a political consultant was a big mistake. "To be clear, everything we did was done according to the law and entirely legitimate," Stephenson added. "But the fact is, our past association with Cohen was a serious misjudgment. In this instance, our Washington D.C. team's vetting process clearly failed, and I take responsibility for that." In that same mea culpa, Stephenson also said AT&T's senior vice president for external and legal affairs, Bob Quinn, "will be retiring." Quinn had started with the old Bell system as a telephone operator in 1980, later went on to become a trial attorney after law school and rejoined AT&T in 1993 as a regional attorney. He had been in charge of the external and legislative affairs group since October 2016, several months before Cohen was hired by that unit. Stephenson said from now on the external and legal affairs group would be reporting to company general counsel David McAtee.

Randall Stephenson, CEO of AT&T speaking at the New York Economic Club on Nov. 29th, 2017. Adam Jeffery | CNBC