GarageBand: Apply an effect to one section of a project.

Hey guys. I'm currently working on a song, and I'm wondering if it's possible to apply an effect to one whole section of a song (the yellow highlighted cycle pictured below), and have said effect cut off as the song kicks in. I'm trying to make the intro sound as if its coming through a telephone or old radio, and when it transitions, the effect stops and the normal sound continues. Any ideas? Or must I do it the long and contrived way? Thanks.