An answer to the existence of recordings of Mark Twian's voice: http://www.telecomtally.com/blog/2006/02/how_did_mark_tw.html
From that site: About a recording of his voice, there is nothing extent that is without doubt a recording of his voice. Thomas Edison did record Twain's voice but those recoding were lost in a fire. Rumors of other recordings come up from time to time but nothing has ever been verified. A recording at Yale is generally thought to be that of a mimic who perhaps knew Twain. The simplest answer is that there are no recordings of Twain's voice.
edit - There may be a more authoritative answer out there somewhere.