Late in the 1980s through 1990s, he held executive positions at the company, including oversight of SBC's investment in Telefonos de Mexico (Telmex), where, according to Bloomberg, he was mentored by Carlos Slim.

[4] In July 2001, he was appointed senior vice president and chief financial officer for SBC, helping the company reduce its net debt from $30 billion to near zero by early 2004.

In 2004, he was named chief operating officer of SBC and also appointed by President Bush as National Security Telecommunications Advisory Committee.

[6] In September 2016, Stephenson gave a speech regarding race relations at AT&T’s annual Employee Resource Group conference in Dallas.

An employee posted a video of the speech to YouTube, in which Stephenson asked attendees to make a greater effort to understand each other and communicate better through a compelling witness defending Black Lives Matter despite racial tensions in the United States.