US Supreme Court upholds §2252A(a)(3)(B) prohibiting offering or soliciting "any material or purported material in a manner that reflects the belief, or that is intended to cause another to believe that the material is illegal child pornography." (http://www.oyez.org/cases/2000-2009/2007/2007_06_694/)
http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=US&vol=00