Kiefer Sutherland, who plays an unseen voice in Colin Farrell's latest movie 'Phone Booth', says he's happy not being seen on screen.

He admits he wouldn't have taken on the lead role, played by Farrell: "I remember saying to him, I don't know that if someone had offered me this I'd have taken it, if I'd have had the courage, because it's ultimately a one-man show."

Farrell plays a New York publicist who picks up a receiver in a phone booth and is told he will be killed if he hangs up.

'Phone Booth' hits screens in the US this Friday, having been postponed after the American sniper attacks last year.

It's due out in Ireland on 18 April.