In the U.S. the term solicitor refers to "A person who seeks business or contributions from others; an advertiser or promoter." Blacks Law Dictionary, 8th Ed. Thus, pretty much all sales people are solicitors and for the most part that is not a crime. In many cities a door to door solicitor needs a local license, however.lol...soliciting in the US is a crime.
The solicitation of prostitution is, of course, illegal in most of the U.S. It's important to specify exactly what is being solicited.