I worked with someone who used a Stephen Hawking style voice application for a while. Its really weird having a conversation with someone like that. There's a delay between everything people say. It's a lot like using IRC on a really laggy connection. I quite enjoyed talking to him because everyone had time to think between while he 'typed'. The point is though, even if the sound his app used was a perfect recreation of his own voice it wouldn't be like talking again. It's a different experience.