In "Coal Miner's Daughter", Beverly D'Angelo played Patsy Cline and sang all her songs, She won a Country Music Association award for Album of the Year......
She did not sound nearly as good as Patsy Cline. Fortunately, the movie was not really about her. Patsy Cline's character was only in the movie because she was a close friend of Loretta Lynn's. I thought Sissy Spacek did a pretty job with Loretta Lynn's songs, but Loretta did not have a voice like Patsy Cline's. If you're making a movie about a singer with one of the great voices of all time, there is no point in using an actor's voice. Beverly may have sung well, but she did not sound like Patsy Cline (IMO).