“Hello, this is Morgan Freeman. I wish I could tell you that Morgan Freeman was available to take your call. I wish I could tell you that, but this is no fairytale world. Morgan Freeman is gone now; to where I cannot say. But if you’re lucky, I might just call ya’ back. Get busy leavin’ your message.”
The only problem I have with the voices is that the French and Spanish ones are really hard to understand. It’s almost like the voices are speaking English words based solely on French and Spanish phonetic rules, instead of sounding like English in a French or Spanish accent. Either way, it was a jolly good time, and I recommend that you at least play with the app, if not actually use it on a regular basis.

Now select “Greeting” in the upper left of the screen. Tap “Custom” and then “Record” to record your personalized voicemail greeting.
On the iPhone, go into voicemail and tap "Greeting". Record a few seconds of something and tap stop. Before you tap save, use iFuntastic or SFTP to navigate to /var/root/Library/Voicemail on your iPhone. You'll see a file called "Greeting. amr". This is the audio you just recorded. Delete that file and replace it with your custom message which should then be renamed to "Greeting.amr". Tap "Play" on the iPhone to verify your message works. If it plays, tap "Save" and your custom message will be uploaded to AT&T's servers.