According to Britney Spears’ official blog, Jordin Sparks will join the second North American leg of the Circus tour as a special guest. Sparks will perform on the U.S. portion including dates in New York City, Los Angeles, Boston, Philadelphia, Miami, Detroit, Chicago and other cities before concluding on Sept. 26 & 27 in Las Vegas.

http://news-briefs.ew.com/2009/08/14/jordin-sparks-joins-britney-spears-circus-tour/