There are several things about this movie that make it special beyond it being Tom Hanks showing his amazing skills in all facets of filmmaking, it also includes the theme song selected for the movie because it was the foundation of the film. In other words, because the movie revolved around a "One Hit Wonder," song, Hanks had to find a song that could actually be a one hit wonder.
Tom decided to give something a try. He put word out that he was looking for a song for a movie that sounded like the Beatles, and of course hundreds of people sent demos hoping for the best. One entry was from a base player in a California band named Adam Schlesinger called "That Thing You Do," and as soon as they heard it, they were hooked.
Then not unlike when they put the Monkees together, Tom had to create a fictional band for the movie. Not only actors of course, but also guys who could do some singing and play various musical instruments or at least fake it really well. They used another singer, not in the film, to sing the song and the band lip synched. Once the song skyrocketed up the charts, he was upset that he wasn't getting enough credit. But a contract is a contract. He sold all rights to his portion of the song when coordinating with the movie studio; bad move on his part as you'll see...