High Quality Content by WIKIPEDIA articles! 1600 Smith Street, (previously named Continental Center I, also known as Cullen Center Plaza) is a 51-story, 732-foot (223 m) office tower in Downtown Houston, Texas, United States. The building houses offices of United Airlines, and it was Continental`s headquarters prior to its merger with United Airlines. At one point it also served as the headquarters of ExpressJet Airlines. It is a part of the Cullen Center complex.