Although I like face recognition, I'd prefer to use voice recognition login. Is it possible? If it's possible how do I setup the software?
No, with the current set of software for Ubuntu, it is not possible to login by voice.
There is no software to allow you to do this. Voice recognition is still a very new and imperfect technology. Everyone can agree it would be cool and high-tech to walk up to your computer, say something, have it say "Access Granted" and log us in. But right now, we can only dream.
To create a secure voice login would require an extraordinary amount of computer power to accurately analyze the voice. Apple's Siri sends the data to servers to have them report back what was said, because it does not have the power to do it on it's own.
However, I think it would be extremely cool and is a great idea. If you would like to get the ball rolling, head over to http://brainstorm.ubuntu.com site and start the discussion there. You'll get feedback from lots of people including Ubuntu developers, and there if enough people think it's a good idea it'll happen.
There are various kinds of voice authentication. For example, doing speech-to-text and then verifying the decoded text; voice pattern analysis; singing a tune; analyzing the frequency spectrum of the voice and so on. Depending on what you are looking for, you are early or very early in the game.
You could allow automatic login with or without a password, and then start some software tool that would prompt and check your voice, speech, anything. For proof of concept purposes, you may start the software from your .login or .bash_rc script, but beware that they may be terminated from the keyboard. If authentication fails, execute logout.
The alternative (the hard way) would be to find or implement a Pluggable Authentication Module (PAM), similar to the fingerprint authentication for TI laptops. Although I can not point you to a ready to use module, it is technically possible.