A friend of mine once interviewed the late Don LaFontaine — the "Voice of God" for zillions of film trailers — and on request Don left him a splendid in-character voicemail.
So this sort of thing must be common to the biz. Because Sadie UltraNeko, who writes Sadie's Gaming Infection, swears these are real voicemails by the bona fide voice actors for Niko Bellic, Solid Snake, Otacon and Duke Nukem wishing her happy birthday.
She's either got tremendous pull — or friends with outstanding voice impression skills. (Come to think of it, Otacon does sound a little like Adam Barenblat to me.) I know, my first thought was these were pieced together from game dialogue. Actually, she got these guys to leave her birthday wishes when she interviewed them earlier, like my pal did with Don. And kudos to the actors, who sound like they put some work into it.
Still, I'm a little peeved I didn't get a call from so much as General Diego (Red Dead Revolver) on my birthday. *sulks*.
UltraNeko's Voicemail [YouTube]