I worked at a broadcast station last summer. You have to do the paperwork before you do the internship. Otherwise, the college's accreditors get upset. Another problem is that the station where you worked was in a more vulnerable legal position if you were not officially signed up for academic credit while you were doing the internship. For example, the IRS wage and hour laws may be a problem.
Students arrange their own internships.
Many of the larger companies have regular internship programs for students. You can write or call the company for applications. If you want to work one summer in your hometown station, the best time to start arranging the internship is over Christmas holidays. Also, information about internships is posted on the department bulletin board.