LEVNET folks had it right. The sound you hear on the soundtrack of "The Station Agent" is not a theremin - it's definitely a musical saw.
It can be heard in a scene midway through the movie where the 3 main characters (Joe, Ilivia, and Fin) are sitting on a train bridge eating beef jerky. It's backed by a ukelele, which sounds like a pretty good combination in my opinion.
Too bad it's not a theremin as we had originally reported. It works well in the soundtrack.
