There's a good article on EW about the journey Anomalisa took from sound play to animated feature. Some choice quotes:

"I said to them, ‘If you can raise the money, sure,’ thinking that nothing was ever going to happen with it because that’s been my experience for the last seven years: that nothing ever happens with anything.”

[...]

Kaufman and Johnson recorded [the cast] together before their puppet avatars were even designed. “We had them in a studio together, and we did it like a play,” says Kaufman. “You can’t do the job where Jennifer comes in one day and David comes in three days later. It’s performances, it’s intimate, it’s people having these moments together.”

[...]

“It came from sort of no expectations,” says Kaufman. “That it did happen, and that we got to make this under the radar completely on our own terms is really one of the highest points of my professional life.” (Source)

Duke Johnson, Tom Noonan and Jennifer Jason Leigh are also quoted in the article. There's a short video interview with the cast, too.