 Late in the 1980s through 1990s, he progressed through a series of leadership positions in finance, including an international assignment in Mexico City overseeing SBT's investment in Telefonos de Mexico (Telmex), where, according to Bloomberg, he was mentored by Carlos Slim.In July 2001, he was appointed chief financial officer for SBC, helping the company reduce its net debt from $30 billion to near zero by early 2004.From 2003 to 2004, Stephenson served as chairman of the board of directors for Cingular Wireless.