In an interview last week with IGN UK, Bettany talked about doing the role:
Recording the voiceover for the first movie took about an hour. Bettany had a great time working with Favreau but completely forgot about recording the lines right after doing so.
I was on the set of Legion. It was the weekend after Iron Man opened, and some of the crew came in and were like, 'Hey, I was listening to Iron Man. You're in Iron Man, right?' 'No, I'm not.' And they said, 'Well, it sounds like you.' And then I went, 'Oh, wait! I am!'
Will we "hear" Jarvis in the second Iron Man? Bettany's not sure. He says he's not sure if he'll be coming back or not. We can assume this means he hasn't recorded any lines yet and not that he's simply forgotten again. I have to admit that when I heard Jarvis' name mentioned in the first, I was a little disappointed. Having Stark's computer system named after the character means we most likely won't actually see Jarvis in the movies. It's not like I'm the biggest Jarvis fan but he's been an important character in the Avengers' history. Now the poor guy probably won't get a chance to cross over to the big screen. Unless the 'real' Jarvis was on vacation and Tony just couldn't bear the thought of being without him and named his computer after Jarvis.
If the first movie only required an hour, there's still a chance Bettany will be called in last minute to record some lines. Do you care if we 'hear' Jarvis in Iron Man 2? The movie opens May 7, 2010.