I think you misheard. Phoenix played Jonny Cash in "Walk the Line" along with Reese Witherspoon who played June Carter Cash.

When I first say the trailers for this film I snorted in digust! Phoenix is more of a tenor than a baritone or base and Witherspoon as his wife? Yikes! I LIKE jonny Cash's music, I have it on my MP3 player, and I couldn't see how the two could pull it off. Well, aparantly they DID, so now I'll have to see the film. The Grouchmate is enthusiastic about seeing it, but I am firmly in character...skeptical!