Actor Joaquin Phoenix often telephoned his Walk the Line co-star Reese Witherspoon in a bid to persuade her to ditch their singing scenes in the movie.

The pair star as Johnny Cash and JUNE CARTER CASH in the hard-hitting biopic of the country singers - and Phoenix was terrified of providing renditions of Cash's classic songs.

Witherspoon was equally panicked, but they both knew to do the film justice they should avoid lip-synching.

Phoenix says, "I spent months rehearsing the singing part and every once in a while I'd think, 'I can't sing this! Why don't I just lip-synch it?' I'd call up Reese and tell her I'd quit the singing bit if she did.

"We'd agree to lip-synch for about five seconds - and then revert back to the singing."